Introduction
Having summarized my own metaphysical principles, I will now attempt to understand the Mahayana conception of 'emptiness' in terms of these principles. This fundamental idea appeared at the beginning of the Mahayana movement, which coincidentally occurred somewhat before the time of Christ. It was emphasized in the famous Prajnaparamita Sutras, which we will examine shortly. The idea of emptiness had a profound influence on all later Mahayana philosophy and thinking, and it was interpreted in a variety of ways. (Indeed, Mahayana Buddhism developed into a living universe of religious inspiration and insight, rather than into a tight and closed system.)
Mahayana was a reform movement within Buddhism that arose around 100 BC, or about 400 years after the death of the historical Buddha (called Shakyamuni). Whereas the earlier Hinayana (or Theravada) tradition concentrated on achieving enlightenment for an elite of monks, in a somewhat austere and conservative way, the Mahayana was filled with a compassionate zeal to bring enlightenment to every conscious being. It placed emphasis on spiritual insight rather than on scholarly philosophy. While the earlier Buddhism stressed wisdom and meditation as a means to attain a rather sober inner peace called 'Nirvana', the Mahayana expanded on this to blossom into a mystical vision of Enlightenment that embraced the entire Universe and every conscious being within it into one blissful and harmonious whole.
I cannot resist pointing out a certain similarity of spirit and feeling between Mahayana and Christianity (or at least the original Christianity of Jesus). There is the same gentleness and wisdom, as well as a sympathetic concern for all humans and an evangelical zeal to 'liberate' them to a pure spiritual life. One can only speculate whether the fact that they were roughly contemporaneous is mere coincidence or something else. The something else may have been the spread of ideas through trade and travel, or it may have been the manifestation of a new stage in the evolution of the consciousness of mankind, perhaps even intended by God. Of course, the notion of God's intervention in history has a distinctly Judaeo-Christian flavor and perhaps represents too much of a digression.
Emptiness can be briefly summarized as the correct spiritual or psychological attitude for achieving enlightenment. (This attitude also has ontological implications, as we will see.) It is supposed to represent a significant advance (or at least change) from the Theravada approach, although similar ideas can be found in the earlier Buddhism. (Really the different schools of thought represent different aspects of the Buddha's original intuition, and the psychological continuity between the schools is much closer than the differences in name and tradition might lead one to suppose.)
Ironically, I have already committed a bit of a 'sin' by calling emptiness an 'idea'. The whole point is to achieve a state of mind that transcends mere concepts, so that our original underlying Buddha Mind can be realized as a living reality, and this is enlightenment. Nevertheless, as rational beings we must resort to some kind of conceptual thinking if we are to discuss it at all, and so we must use words and ideas. Of course, my understanding can only be incomplete, finite being that I am, but I will try to quote enough scripture to give my interpretation plausibility.
The idea of emptiness held a curious fascination for me many years ago, when I was a philosophy student, even though I found it quite confusing. I think that many Buddhists today continue to be confused, and many of the books that I have read on it do not really provide a satisfying explanation, at least not to me. However, some of what has been written is quite clear, and it is not a completely hopeless task to acquire some insight, even if we have not spent many years in deep meditation.
Nowadays, I think that I have at least a handle on the idea of emptiness. In fact, I believe that it is quite compatible with the 'idealistic' metaphysics presented above (i.e. the philosophical principle that everything is consciousness). Indeed, there is an important Buddhist tradition (Yogacara) that can only be described as idealistic, and many other Buddhist traditions such as Zen have a strong idealistic flavor, with many famous masters making unmistakably idealistic pronouncements. Nevertheless, I should warn you that many Buddhists refrain from going quite so far as to embrace 'Subjective Idealism' - the philosophical view that only consciousness exists.
Amusingly enough, the important and seminal Buddhist tradition of Prajnaparamita (Perfection of Wisdom) or 'transcendental wisdom', which gave us the Prajnaparamita Sutras, would say that nothing exists (or that nothing exists inherently), and this is the true meaning of emptiness. I will argue that this, too, is implicit Idealism, coming from visionaries who were more interested in celebrating a fresh view of enlightenment than in analyzing it with philosophical precision. At least this was true initially, around the beginning of the Common Era, when the Prajnaparamita scriptures first appeared, along with the birth of the Mahayana.
The Prajnaparamita literature includes such well known texts as the brief Heart Sutra, recited everyday in Buddhist temples around the world, the pamphlet-sized Diamond Sutra, and the Prajnaparamita Sutras in 8,000, 18,000, 25,000, or even 100,000 lines (as well as other lengths). (There is also a Prajnaparamita Sutra consisting of the single letter 'A'!) A number of translations of the Heart and Diamond Sutras are available on the web. For many years, the Prajnaparamita Sutras were considered too obscure and scholarly for mere mortals, but a new translation by Lex Hixon called Mother of the Buddhas is quite elegant and readable.
Later, famous commentators, such as Nagarjuna (2nd century AD), tried to give the somewhat cryptic Prajnaparamita statements a philosophical basis. In the following, I will emphasize the Prajnaparamita inspiration itself, by quoting from it and applying my own interpretation. Understanding the commentaries is made complicated, in my opinion, by the fact that they are enmeshed in the same philosophical confusion that has plagued Western philosophy, such as the meaning of 'substance' and 'causation'.
To tell the truth, I am misrepresenting Nagarjuna. He was really arguing against the views of other contemporary philosophers, rather than propounding a specific view of his own. However, his actual writings are often obscure, and much of the literature surrounding his interpretation of emptiness is philosophically flawed and confusing. It gives me a headache to read or discuss it! Nevertheless, I will discuss the closely related topic of dependent origination in the next section, without specifically addressing Nagarjuna's writings.
The essence of emptiness, according to my view, is that True Reality is one vast, pure, infinite and blissful consciousness, and that we realize this reality when our mind is empty, that is, wiped clean of any trace of discriminative or dualistic thinking. This does not mean that our mind becomes blank and that we become like stones. On the contrary, our mind becomes pure and vast as space itself (and space is indeed a common simile for enlightenment in the Prajnaparamita literature). This nondualistic consciousness means that we do not discriminate between subject and object (i.e. between ourselves and the world), and neither do we discriminate different 'things' in the world. In this way, we eventually reach the pure and 'mystical' state of consciousness, after all of the roots of dualistic thinking hidden deep within our subconscious have been eradicated. These roots have developed over many years, or even lifetimes, nourished by deluded thinking, clinging attachments, and poisonous passions, and so 'dissolving' them may take many years of meditation and 'mindfulness'.
A rich source of material on nondualistic philosophy is the Realization.org website, especially the references to 'Advaita Vedanta' and to 'realized' masters such as Ramana Maharshi and Nisargadatta. See also the Nonduality Salon. The fact that the Advaita Vedanta and the two names just cited belong to 'Hinduism' should not matter if the truth is one, as it must be by definition. Mahayana Buddhism and Advaita Vedanta are historically and spiritually intertwined, and the leading proponent of Advaita, the 8th-9th century Indian philosopher Sankara, has even been accused of being a 'crypto-Buddhist' by his detractors.
Of course, the same shapes and colors as presently in our consciousness will continue to manifest after we become enlightened. As I said before, I could never tolerate a philosophy so absurd as to claim otherwise. However, our attitude towards these shapes and colors changes dramatically, and this leads to a profound transformation of our entire consciousness.
And of course, for any proponent of Idealism, a profound change in consciousness must imply a profound change in ontology. This will help us to understand why the Mahayana maintains that, not only must our mind be 'empty' (of ego and concepts), but also the entire world should be viewed as 'empty' (of inherent or substantial existence). This has caused considerable confusion for countless students of Buddhism and led to the notion that 'emptiness' is perhaps an irrational or nihilistic concept, possibly even a concept that is dangerous to our sanity!
A Key Point
Above all, I wish to avoid confusion in the mind of the reader regarding this curious notion of 'Emptiness'. Such confusion arises because our discriminating mind cannot resist asking questions such as: What is it? Why? How? What does it look like? Show me. And so on. Indeed, what does it mean to 'understand' it unless we answer these questions? However, the Mahayana scriptures will insist that it cannot be truly understood until it is experienced, and then it is more a question of 'realization' than conceptual understanding.
So, I think that it would be helpful always to keep the following observation in mind. There is a universal school of 'mystical' literature in the world (Mahayana, Advaita, Eckhart, Sufiism, and so forth) that asserts the existence of a 'higher' state of consciousness that can best be described as 'non-dualistic'. It is 'higher', because, among other things, it is free of discord and suffering and is permeated by peace, bliss and illumination. (Who wouldn't like that?) It is 'non-dualistic', because our ordinary discrimination of experience into subject and object, ego and world, and of the world into separate 'things', somehow vanishes, even though the 'shapes and colors' remain the same. Non-dualism and emptiness are essentially the same thing. A non-dualistic consciousness is 'empty' of any kind of discrimination.
Just what this might mean is discussed further in many places on my philosophy pages. But if we are willing to have faith in these numerous mystics - acquired through the sincerity and authority that permeates their recorded texts - then we should begin by at least accepting this state of consciousness as a psychological reality. Only then should we try to understand it, in so far as it can be understood at all. Any further ontological interpretations, such as the ones offered here, might be considered helpful, but the reality of the experience is what ultimately matters.
Remember the 'noble silence' of the Buddha, who refused to be drawn into metaphysical arguments. Instead, he emphasized the actual realization of our spiritual potential, through self-control and meditation. In this light, the 'anti-conceptual' tendencies of the Prajnaparamita harmonize with the Buddha's original attitude.

Dependent Origination
In many books on Buddhism, an explanation of emptiness is provided in terms of the concept of 'dependent origination', which was part of the Buddha's original teaching. In particular, the famous Mahayana philosopher Nagarjuna based his argument for emptiness on dependent origination. It is my opinion that this point of view, insofar as I understand it, is not satisfying and does not express the deeper meaning of emptiness. I will briefly state my reasons, but please bear in mind that I have not studied this aspect of Buddhism as deeply as I would have liked, and I may be mistaken about some basic points. So the following is only something to keep in mind when you read other Buddhist texts. (Indeed, this is the case for everything that I write!)
Dependent origination, also called 'conditioned arising', basically says that everything happens for a reason or cause: If event A happens, then event B will follow. (Note that this is essentially the same as the concept of causation of the famous British philosopher Hume.) Dependent origination, or causation, provides a way - some would say the way - of understanding experience. Events do not happen because of blind chance or because of the whims of gods; they happen because of preceding events. There is a one-to-one correspondence between successive events, provided we know all the details. This view is also called 'determinism'. (Let's ignore the indeterminism of Quantum Mechanics for now. Also, see my Philosophy Page for a discussion of so-called 'free will' and its relation to determinism.)
The Buddha was particularly interested in applying this understanding of experience to our psyche in order to relieve our discontent. His 'psychology' says that our present condition is determined by our past intentions and behavior. This is called karma, the fruit of past intentions and actions. If we continue to see everything in terms of our self, if we have excessive attachments to transient things, if we are ignorant that true happiness comes from a peaceful mind and not from a desperate attempt to satisfy every insatiable desire, then we will continue to dwell in self-created frustration and discontent. This manifests itself both in our internal psychological state and in terms of the world into which we are born. We become enlightened as we calm our minds and hearts, dissolve clinging attachments to objects and ideas, and recover the inherent purity and bliss of our 'true inner nature'.
To be precise, we should say that dependent origination is true for all events in Samsara, that is, in the phenomenal world of everyday experience. It does seem that every event that happens in the world of perception, or even in the internal world of thoughts and feelings, is correlated with other preceding events. The framework of causation is essential for science, which could not proceed without it. (Even quantum mechanics uses a deterministic Schrodinger equation to describe the evolution of a 'probability cloud' of subatomic particles.) However, it may be that a consciousness that is 'liberated' from Samsara through enlightenment is also released from cause and effect. Some Buddhists seem to believe this. Or perhaps the enlightened mind is still subject to cause and effect, but because of wisdom and insight, it skillfully navigates the world of Samsara without generating further destructive karma.
So far we have discussed the Buddha's original teaching regarding dependent origination. Now we come to the application of this concept to the Mahayana teaching of 'emptiness'. Many Buddhists try to explain emptiness in terms of dependent origination, often to the point where the two are virtually identified. The basic idea seems to be that everything is dependent on everything else, so that nothing has an 'inherent existence'. This lack of inherent existence is said to be the same as emptiness. Realizing this lack of inherent existence provides the wisdom that leads somehow to enlightenment. Perhaps by becoming aware of our lack of inherent existence, as well as that of all objects that we perceive, the bonds of attachment are dissolved, through some psychological or spiritual process.
Without going into too much detail, let me briefly say why I do not consider this explanation of emptiness to be useful or convincing. Basically, my feeling is that dependent origination is entirely compatible with the philosophy of materialism, which says that only discrete material objects exist behaving according to cause and effect. Therefore, the realization of the truth of dependent origination is not, in itself, sufficient to lead us to an attitude or philosophy other than that of materialism. In particular, materialism tends to deny (or at least to be highly skeptical of) the existence of 'spiritual' entities such as consciousness, spirit, afterlife, God and so forth. At most, consciousness is allowed as a mere 'epiphenomenon' of the brain, the 'ghost in the machine' that disappears when we die and our brain decays (or loses blood and oxygen).
It may be true that realizing the dependence of everything on everything else fosters a less self-centered and more compassionate attitude, which is conducive to the spirituality that Buddhism is trying to inculcate in us. However, this does not explain the rather peculiar notion of 'emptiness', in my opinion. Why can we not become kind, loving, and altruistic without such a recondite notion as that of emptiness? Many religions achieve this kind of spirituality without introducing such a rarefied and abstract idea. There must be something more to emptiness.

Idealistic Interpretation
Indeed, I feel quite convinced that the idea of 'emptiness' was introduced to describe a psychological state attained during deep meditation (and carried over into everyday life). As explained above, when our consciousness is completely free of its usual dualistic thinking, i.e. in terms of self and objects, then a transformation of consciousness occurs which is pure, blissful, compassionate, beautiful, deeply satisfying, and has an experiential quality or flavor of expansiveness such that the word 'emptiness' seems like a good metaphor. When the usual conceptual and psychological barriers between ourself and the world break down, all of reality appears as one vast and pure 'thusness' or 'suchness' (to use common Mahayana terms), which is also often described in the Prajnaparamita literature as 'like space' or 'like a dream'.
Really, this vast and pure 'thusness' is not different from consciousness, after the latter has been purged of discriminative notions such as 'self' and 'other', 'like' and 'dislike', or anything else that disturbs its unity, purity and harmony. When consciousness is in a state of perfect calm and nondiscrimination, its 'original nature' is recovered, and this evidently radiates bliss from deep within, somewhat as the calm surface of a lake reflects the sky. The 'emptiness' in question is the lack of conceptual barriers, such as self and other, which produce disquiet in the mind. This disquiet, or lack of unity, in turn produces our ordinary and 'unmystical' state of consciousness, according to the almost universal testimony of mystics. Of course, the enlightened person sees the same shapes and colors as the unenlightened person, only his attitude and psychological reactions have fundamentally changed, and this produces a profound change in his overall 'state of consciousness'.
The 'lack of inherent existence' of self and objects, propounded so often in Buddhist literature, would seem to be the same as the present 'idealistic' view of true reality as one vast and pure consciousness, uncontaminated by discriminative thinking. It is true that most Buddhist authors do not argue specifically in terms of idealism, the philosophy that everything is consciousness, although some do. However, I believe that the denial of 'inherent existence' is really the same as the denial of discrete material objects external to the mind. The 'inherent existence' is what Western philosophers call 'material substance'. I can see no other reasonable explanation. The 'emptiness' that remains when inherent existence or material substance is denied is the same as consciousness, for what else if left? Surely, phenomena continue to appear, but they appear in consciousness only. Also, with no 'external objects' to juxtapose against the 'self', how can a concept of self remain? The dissolution of all conceptual boundaries achieves the aim of the original Buddhism, and perhaps more.
Some would say that I am thinking too much in terms of 'ontology' and not enough in terms of 'soteriology'. That is, the doctrine of emptiness is intended primarily as a kind of spiritual medicine, as a remedial attitude towards experience that leads to a transformation of consciousness, rather than as a statement of how the world actually 'is'. I would respond by saying that how we perceive the world and how the world really is are not two different things. Instead, they are closely related. (This idea can be found in the Buddhist scriptures. For example, what appears as water to humans seems like ambrosia to the gods and like filth to the demons.) If only consciousness exists, then there must necessarily be a close relationship between the two.
The argument for emptiness based on dependent origination does have the following virtue. It may be one of the best ways of inducing the 'egoless' state of mind advocated by Buddhism for those who still believe in some kind of materialism (i.e. in some kind of 'objective reality' independent of consciousness). Many people will continue to believe this, because it is so deeply ingrained in our thinking. The argument for emptiness based on dependent origination then suggests that we meditate on all things as being composed of parts, that arise based on conditions and causes. In this way, all 'entities' in the world are dissolved into atoms and conditions and deprived of 'inherent existence', of absolute existence 'from their own side' as the Tibetans like to say. (Indeed, the argument for emptiness based on dependent origination is quite popular in certain Tibetan schools, and for this reason has found its way into much of the popular Buddhist literature.)
Really this view has much in common with some words from the Old Testament, namely, 'ashes to ashes and dust to dust'. In other words, if there were a material world, we would still have to admit that we have a brief life in a fragile body, that is made of dust, and that will return to dust. Any kind of pride or ego is foolishness, a kind of delusion similar to that of an actor who believes that he really is the king that he is playing. The famous words from Shakespeare's play Macbeth have a strong Buddhist ring to them,

To-morrow, and to-morrow, and to-morrow,
Creeps in this petty pace from day to day
To the last syllable of recorded time,
And all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
Signifying nothing.
The difference is that for Shakespeare, this view is merely depressing, whereas for Buddhism, it is the key to liberation. And whether one views emptiness from the standpoint of 'consciousness only', or from the standpoint of dependent origination applied to an external world, the basic psychological motivation is the same, namely, to purge our instinctive tendency to see the world as composed of independent, self-sustaining 'things' with a permanent solidity and sharp boundaries between them. The culmination of this attitude, according to Buddhism, is the egoistic view of our petty self as the supreme 'thing' around which all else revolves. This deeply felt attitude, by its very nature, obstructs the enlightened state of mind, and results, sooner or later, in tension, frustration, depression, conflict and the loss of the bliss and energy of the purified mind of enlightenment.
It should be realized that this nondual philosophy of 'dissolution of conceptual boundaries' only becomes effective when it has penetrated into the deepest recesses of our 'subconscious'. This is achieved through years of meditation. It does not arise through a few minutes of idle speculation. We must understand that, although Buddhism has implications for the 'armchair philosophy' of academia, it is primarily concerned with a deep transformation of the roots of consciousness. So when I say that concepts of 'self' and 'other' affect our state of mind, I am referring to the predispositions and tendencies buried deep in our minds through years or even lifetimes of such thinking. We have towards our experience a deeply ingrained 'reactive' mentality that we take so much for granted that it is practically invisible to us. We must become much more sensitive to our inner mind and feelings before we can start to make spiritual progress.
It must also be emphasized that no sane Buddhist wants to preclude our ability to think rationally about daily events so that we may deal appropriately with the mundane necessities of life. We must of course use some degree of conceptual thinking in order to get up, get washed, get dressed, go to work, eat and otherwise live. However, behind all this, or over and above all this, there should be a pure nondiscriminative awareness that views the spectacle of life like clouds passing across the sky (a metaphor found in some Buddhist scriptures). Above all, we must eliminate concepts and judgments that lead to deep subconscious tendencies, predispositions, and blind reactions to daily events, and which affect our overall state of mind and obstruct the blossoming of enlightenment. I cannot claim to fully understand all of this, but I have a considerable degree of faith that this can be achieved, based on my limited experience and on a respect for enlightened 'masters' that I have acquired through extended reading (and reflection upon this reading). To be more precise, I have acquired faith in their experience, and I am trying to understand the ideas that they derive from this vivid - indeed overwhelming - experience as best I can.
The main stumbling block in the word 'emptiness', at least for those raised in a Western tradition, is that it seems to refer to 'nothing', so that a kind of nihilism is suggested. In fact, the authors of the Prajnaparamita literature were also aware of this pitfall and constantly warn against a nihilistic interpretation. I think it would be helpful to consider 'emptiness' as synonymous with 'space', provided this denotes the state of consciousness just described rather than an external entity. Indeed, according to my idealistic philosophy, there are no external realities; there is only consciousness. So space and consciousness are in fact the same, and the word 'space' is more than a mere metaphor. The important point to remember is that consciousness has been raised to a much higher state than the one to which we are accustomed, due to the transformation brought about by the purging of our psychological bondage to dualistic thinking.
It is worth emphasizing that the removal of psychological obstructions, which originate from the belief in and attachment to discriminative concepts such as 'self' and 'other', leads to a transformation of our entire consciousness - a transformation that affects thought, feeling and perception. So not only do the enlightened identify (or embrace) at a perceptual level with all of space (and all beings in space), but I strongly suspect that they also acquire a blissful, floating, euphoric feeling that has the 'taste' of space. If 'space' is a synonym for both emptiness and consciousness, then we can see how this 'experience of infinity' permeates all aspects of consciousness. (This reminds me of something funny attributed to the famous Japanese Buddhist scholar D.T. Suzuki. He said that enlightenment was like everyday consciousness but 'two inches above the ground'.)
Furthermore, I do not think that the only good feeling is the emotion of euphoria. To the enlightened, perception itself probably also has its associated good feeling, which I imagine as a kind of 'sublime quiescence'. Indeed, the feeling of sublime quiescence suffuses all of consciousness, spreading a 'cool and beautiful blissfulness' everywhere, and ultimately becomes indistinguishable from emptiness itself. At least, this is how I imagine it, for some reason; my intuition and readings suggest this to me, even though I do not have the actual experience. Emptiness, purified consciousness, blissful quiescence - all these are different names for the same 'transcendent' experience.
And again, to avoid needless confusion, it is essential to remember that concepts are to be used when appropriate. It is really our psychological attachment to concepts (or discriminations) that must be eradicated - e.g. our identification with our body (or thoughts or emotions) rather than with all of reality, with all of consciousness, with the entire universe, with Buddha, with the Dharmakaya, with God, with the One Reality, with the One Mind (see my Avatamsaka Page for further elaboration). The concepts that we use to live and get by then become mere neutral images passing across the sky (or screen) of purified consciousness, as are all other elements of consciousness (all of our thoughts, feelings and perceptions). The fundamental reality is then the one vast and purified consciousness containing all 'things' as mere transient images; we no longer see a world consisting essentially of discrete objects each having an ultimate reality. The one reality is the vast emptiness of consciousness.
In fact, insight into the psychological process of 'identification' may provide one of the clearest ways to understand how we can use concepts appropriately while maintaining the nondiscriminative and nondualistic awareness that virtually all mystics consider essential to achieving higher states of consciousness. The perception of the body is still there, and we may even think about it, but we do not identify with it. We either identify with all of consciousness, including all other conscious beings, or we transcend any notion of identification and simply merge with the pure thusness of consciousness.
It is common experience that our identification with finite things - thoughts, symbols, feelings, body, property, accomplishments, social position, social group, nation, or any other object of the discriminative mind - nourishes deep subconscious currents and roots, which then affect how we interpret and react to events, thus setting up a pernicious feedback loop in our psyche. Feelings and prejudices are the concrete manifestation of the subconscious currents, which bind us and pervert our mind, so that we fall far from a state of enlightenment. We then spend our life justifying ourselves and in conflict with others. Emptying our spirit of all of this garbage, throwing it all overboard, may be one of the most 'down-to-earth' interpretations of emptiness, which nevertheless goes to the heart of Buddhism and any true spirituality. Emptiness is freedom, bliss and reality.

Excerpts from the Prajnaparamita Sutra in 8,000 Lines
with commentary

The Prajnaparamita (Perfect Wisdom) literature could be called the 'Mother of the Mahayana'. This voluminous and inspired collection of Sutras (scriptures), dating from about a century before Christ (or about 400 years after the death of the historical Buddha) to several centuries after Christ, expounds the closely related 'doctrines' of Perfect Wisdom and emptiness in texts of varying length, from the single letter 'A', to a short chant (the Heart Sutra), recited everyday in Buddhist temples around the world, to the pamphlet-sized Diamond Sutra, to massive scrolls of verses containing 8,000, 18,000, 25,000 or even 100,000 lines.
This literature is truly the motherlode of the Mahayana vision. Indeed, Perfect Wisdom, poetically represented as a goddess, has been called 'Mother of the Buddhas'. In particular, Prajnaparamita is the foundation of the famous Chan (Zen) lineage of direct (rather than scholarly) insight into enlightenment. Hence, it is appropriate that Lex Hixon's translation of excerpts from the seminal Prajnaparamita Sutra in 8,000 Lines should be called Mother of the Buddhas. It is from this translation that I shall quote and upon which I shall comment.
The earlier translation by Edward Conze was a work of dry, careful scholarship, which was appropriate for its time. Lex Hixon's translation is more 'literary', and in the opinion of many (including myself), it captures the beauty of the original inspiration in clear and elegant language. I now feel that the ice is starting to melt for me on this once forbidding yet tantalizing expression of mystical vision.
Since Lex earned a Ph.D. in Religious Studies at Columbia University, I am satisfied that the translation is sufficiently accurate, even if the back cover of the book warns us that it is not intended as scholarship but rather as a 'contemplative expansion'. And the fact that Lex studied intensively under a variety of Buddhist and other spiritual masters enables me to have confidence in his interpretations and colorations. In the following, quotations from the book are given in purple and my comments in black. The section headings corresponds to chapters in the book.

Mahayana is Immeasurability
Buddha: Mahayana is synonymous with immeasurability. Immeasurability is synonymous with infinity, and infinity with ineffability. ...
These are the first lines of the book. Even if they seem puzzling, we should appreciate their grandeur and sweep, which is characteristic of this entire scripture. Already we sense the vastness of what is surely a 'mystical' vision.
Notice that we start with a pronouncement on the Mahayana, rather than, say, a definition of Perfect Wisdom. Mahayana is the 'great vehicle' that will carry all willing conscious beings to enlightenment. One of the main themes of the Mahayana is that the insight into Reality provided by Perfect Wisdom is not separate from the compassion that seeks to enlighten all beings. Enlightenment is not for oneself alone. It is not just a matter of mundane generosity, but at a deeper level it is the realization that we are all connected through the Universal Mind discussed on my Philosophy Page and recapitulated here. (The extent to which my notions of Universal Mind agree with the Prajnaparamita literature and with Mahayana in general can only be determined as my various Mahayana pages develop over time.)
With this in mind, the words 'immeasurable' and 'infinite' can be understood at different levels. On the one hand, it is the wonderful vision of a vast cosmic ship carrying blinded and suffering souls to a heavenly realm of peace and bliss, which is not to be found on any planet but rather in the purification of the spirit, so that its inherent luminosity may shine forth. But on the other hand, it is the vastness of the vision itself, which knows no restrictions imposed by dogma, by preconceptions, by merely conceptual thinking, by particular points of view, or by any attempt to contain in a bottle. It is a vision that embraces the universe while 'transcending' it, in some sense, that can ultimately only be understood at an intuitive level, acquired through spiritual development.
Hence the 'ineffability' of the vision. The celebration of a vision which cannot be described in words will be one of the key paradoxical themes of this scripture! It is also a common theme of mysticism in general. Nevertheless, I believe that we will be able to learn something and acquire some inspiration by studying these verses. Otherwise, why would the authors have bothered to write them!
The courageous diamond being, the bodhisattva who travels in this vehicle of immeasurability, is therefore traveling nowhere. Nor is there any separate traveler. Nor does this uncontainable vehicle move through any substantial realm. Simply by its perfect freedom from all notions of location, substance and limitation, the Mahayana already abides as omnipresence and omniscience. No separately self-existing personality is traveling on the Great Vehicle, has ever traveled on the Great Vehicle, or will ever travel on the Great Vehicle. Neither the personality structure of the traveler nor the philosophical structure of the Mahayana possess even an atom of substantial or independent self-existence.
Therefore, neither practitioner nor practice can be grasped, crystallized or objectified in any way. What transparent structure can travel in what transparent vehicle?
These lines can be considered a condensation of the entire scripture. They are also quite obscure to the newcomer. Even experienced readers cannot claim to have penetrated their full depth, unless they are already Buddhas! So it will be appropriate to comment on them at some length, to the best of my ability and insight.
The bodhisattva ('enlightenment being') is a Buddha-in-training, who has vowed to relinquish ultimate Nirvana (heavenly escape from the world of suffering) until all conscious beings have been enlightened. Hence, the bodhisattva has a motherly concern for all beings, as does Mother Prajnaparamita herself. The bodhisattva is guiding beings on to the vehicle of the Mahayana, which will deliver them from delusion into enlightenment.
But what does it mean to say that there is no 'separate traveler', who is 'traveling nowhere', through 'no substantial realm'? This is our first allusion to the core of Perfect Wisdom, namely, the notion of the 'emptiness' of all things. The historical Buddha taught the 'emptiness' or unreality of our ego, of our sense of self. The Mahayana expanded this notion into the emptiness or unreality of all things, and it claimed that this was implicit in the Buddha's original message but was held back, because people were not yet mature enough to understand.
In the introductory sections above I discussed my interpretation of 'emptiness' - the Mahayana word that encapsulates the entire vision of this scripture. It is the non-discriminative attitude that sees all reality as one infinite consciousness or 'thusness'. It is the pure, original 'Buddha Mind' - pure awareness itself - that underlies (and sustains) our everyday dualistic awareness and that is retrieved through the stilling of the mind and the abandonment of all preconceptions and mental reactions that try to divide the immediacy of experience into discrete 'objects' seemingly in isolation from each other. The 'mother' of all discriminations is of course the distinction between self and world, which feeds that powerful whirlpool of negative energy called the 'ego'.
This is not to deny that common sense distinctions may be made between tables and chairs. Only we must not allow our mind to indulge its predisposition to becoming addicted to discrimination, to constantly identifying and grasping at objects, so that this mentality colors our entire outlook at a deep instinctive level and traps us in our ordinary unenlightened state of consciousness. (My belief that nondualistic awareness is the precondition for the enlightened state of consciousness is based on my confidence in the pervasive mystical testimony of mankind.)
The identification of objects leads to our identification with objects, in particular the body. This in turn sets us in opposition to other objects. At a practical level, endless conflict may be generated, requiring morality and self-restraint. But at a deeper and more psychological level, we harm ourselves simply by disturbing the purity and calm of our own consciousness, like throwing a rock on a pond. A calm mind - one that is calm and detached and purged of all restlessness at a deep subconscious level - can then experience the bliss and peace inherent in the very nature of pure consciousness, much as the surface of a quiet pond can reflect the blue sky.
Now the identification of discrete objects is closely related to our attribution of reality to them. To say that a table is real, according to the common view, is to believe that it is a discrete, material object, distinct from our mind, and isolated and self-contained from other discrete, material objects. This deeply-rooted psychological tendency to discriminate and identify discrete, independent objects and attribute reality to them reaches its culmination in our utter faith in the reality of our own self, of our own ego.
However, as we have discussed, there is only one consciousness; there are no discrete material objects. (Even the ego is conceived of as a discrete, material object in that we tend to identify ourselves with our body.) These are only powerful illusions, as discussed at length on my Philosophy Page and recapitulated here. (To be precise, we might have to allow for a distinction between your consciousness and mine, although I believe that these are also ultimately manifestations of the single Universal Consciousness or Buddha Mind, as explained on my philosophy pages.)
So what seems like a harmless ontology - the belief that the world is ultimately made of discrete material objects - is closely related to our spiritual imperfection, according to the wisdom of this and similar scriptures. Ontology is not harmless! Ignorance is the cause of bondage to Samsara! Of course, at a practical level, we must interact with our experience as though it were made of discrete objects, but we must not allow this view to seep into the deepest recesses of our mind and become our belief of how reality ultimately is. This has psychological repercussions that prevent the blossoming of a higher state of consciousness, that discovered by Shakyamuni under the Boddhi tree.
Hence, the paradoxical statements like the one quoted above, which can be found on almost every one of the thousands of pages of the Prajnaparamita Sutras. Reality is denied to the most common-sense objects, because this is how the enlightened awareness sees the world. The shapes and colors are the same; if anything, they are intensified as the enlightened mind enjoys its greatly increased sensitivity. However, to the enlightened mind, the fundamental reality is the one vast consciousness or 'thusness'; the so-called 'objects' are like clouds passing across the pure blue sky of consciousness.
And not only are there no objects. There is also no 'space' containing the objects, which explains why the bodhisattva is traveling 'nowhere'. As explained on my philosophy pages, space, conceived of as something external to the mind, must be denied along with objects external to the mind. They are intimately linked, two sides of the same coin, so that if one goes, then so must the other. Space is within consciousness; consciousness is not within space. Space is as much of an illusion as the apparent objects of perception that seem to be contained within space. (However, as I explained above, we can view Thusness or Emptiness as being like space, provided we do not confuse this with the external space of materialism.)
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Subhuti: Buddha, bodhisattva, prajnaparamita - these are merely abstract terms, composed of certain sounds and letters, correlated with certain conventional perceptions and concepts. What they point at has never substantially come into being. What they indicate is an uncreated and, hence, ungraspable and unthinkable presence. The same is true of the terms self and universe. ... That all structures and processes have never been created simply means that they appear vividly and function coherently without possessing any independent essence that can be isolated, grasped or formulated in anyway.
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The absence of the substantial creation of any form is not different from the radiantly transparent, harmonious and coherent functioning of all forms. Thus absolute openness and relative functioning are not divided. They are not two alternative dimensions, but utter simplicity. If one labels and thereby experiences this expansive simplicity as material form and personal consciousness, one is foolishly numbering and labeling that which has no multiplicity and no identity.

Some temporary out-of-place notes:
Enlightenment is the immediate apprehension of the shining miracle of consciousness as it is, before discrimination has reduced it to the 'dead' world of objects that is our ordinary mind. The discriminative mentality first divides the world into 'self' (ego) and 'other' and then divides the other into many 'things'. Turning a raw appearance into an object in this way evidently 'kills' it, due to some subtle yet profound psychological process. The mystery and magic of fresh perception are replaced by the reactive thought, 'It is just a this, it is just a that'. We recapture some of the fresh perception when we see some beautiful or awesome sight of nature for the first time, such as the first time we see the Milky Way. But even the most beautiful and mysterious sight will become jaded as we grow accustomed to it, and our mind says, 'It is just the Milky Way'. The mind of a child is full of wonder; the mind of an adult rarely is.
The conceptual transformation of raw experience into 'dead objects' is closely related to the belief that the world is made of dead matter (rather than living consciousness). In turn, the psychological process of objectification has its roots in our sense of self, which is the 'mother' of all objectifications.
The mystical state would seem to be simply Pure Awareness (or 'Pure Presence' or 'Suchness' or 'Thusness'), which is cultivated simply by being aware - purely, constantly, and without discrimination or conceptual distraction or confusion. Perhaps the Buddhist exercise of 'mindfulness' is intended to cultivate, purify and intensify awareness, to lift it from its present state of torpor. Are not muscles developed through exercise?
Also, the 'Perfect Wisdom' that produces 'Pure Awareness' is not ultimately different from this awareness. They only seem different while we are still on the path, and we speak conventionally of using the former to attain the latter.
Prajnaparamita may not mention the word 'God', but Perfect Wisdom would seem to be the 'vision' of God (i.e. God's vision or awareness). That is, it is the purified awareness of any more highly developed spiritual being, ultimately culminating in a state of perfection that we may call 'God'. Since dualistic thinking has been transcended, it makes no sense to ask whether we are having a vision of God, or whether 'God' is manifesting himself (or itself) in our awareness. Indeed, there ultimately is no distinction between awareness and what we are aware of, whether this be the 'Universe' or 'God'. There are no distinctions at all; there is just one pure and 'unitary' experience, which we may call 'consciousness' or 'pure consciousness'.
This is all in accord with the philosophical principles that I have developed on my Philosophy Page. But let me hasten to add that, in the present context, these philosophical ideas should be considered merely as a dry and abstract 'explanation' or 'logical verification' of an intense spiritual and psychological process. This is not to deny the validity of these ideas; only we must not be content with mere ideas, which are only copies of reality.
So by now you have some idea how I interpret this scripture in the light of my idealistic metaphysics, which says that consciousness is everything. However, problems can still arise with the use of a word such as 'consciousness', since so many people feel the need to think that consciousness must be consciousness of something, which in turn seems to imply a distinction between consciousness and the object of consciousness. This helps to explain the insistence of this scripture on transcending conceptual discrimination, which was taken up by Chan and Zen.

Unthinkable and Unfindable
Shariputra: Revered brother disciple of the Lord, though luminous and transparent, are not the thinking subject, the thought and its object still some reality which actually exists?
Subhuti: Can assertions such as it exists or it does not exist apply to pure presence, which is entirely without modification and hence remains untouched by any possible discrimination or definition?
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The Reality to which these and all other terms [bodhisattva and prajnaparamita] refer is ungraspable and inconceivable, possessing no physical or metaphysical self-existence.
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The adamantine awareness who flows as Perfect Wisdom does not define, formulate and thereby experience Reality in terms of personal forms, personal feelings or personal consciousness. ... Whoever remains crystallized as personality cannot melt and flow as the Perfection of Wisdom. ... One can never blossom into the omniscience which is total awakeness. Prajnaparamita never attempts to grasp or define What Is. Prajnaparamita can never be grasped or defined. With selfless freedom and openness alone can the bodhisattva truly flow as Perfect Wisdom.
The transcendent insight of the diamond being is called the vision which simultaneously sees and sees through all subjective and objective structures without remaining to grasp or even encounter them. This gnostic vision is limitless, unwavering, sublime. ...
Obviously, omniscience cannot be grasped. By its very allness, it is precluded from possessing any particular mark, sign or limit which the mind might cognize or even attempt to cognize. If total awakeness manifested a sign by which it could be defined, discriminated and separately encountered, it would not be total. ... The omniscience or total awakeness of Buddhahood can simply not be located or formulated.
Taking as sole guideline the true nature of all structures, which is the absence in them of any substantial self-existence, one should generate powerful conviction concerning the essential selflessness and signlessness of What Is, so as no longer to assume, even unconsciously or instinctively, the independent self-existence of any structure which one might then attempt to grasp, isolate, cognize and encounter separately. One should not attempt to encounter separately some state of final release, or Nirvana, because desiring or even acknowledging final release implies that there exists some independent structure of consciousness which is released at a certain moment. There is only Prajnaparamita.
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Shariputra: And still there is a bodhisattva who, cultivating this Perfect Wisdom, will attain omniscience?
Subhuti: My noble brother, of course there is! Simply by this clear recognition that no processes, structures or characteristics of any kind are substantially generated, the bodhisattva blossoms as total awakeness. The thought flow and even the physical body of an awakened bodhisattva become perfectly pure, because they manifest solely for the sake of guiding and maturing all conscious beings. With body and thought flow completely purified from subtle egocentricity, the bodhisattva, who actually embodies the omniscience of Prajnaparamita, will meet spontaneously with living Buddhas upon all planes of being and awareness.
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The awakened bodhisattva does not indulge in analyzing and constantly reviewing the skandhas, or structural processes of personality, nor even in contemplating the advanced notions that the skandhas themselves are mere signs. Much less does the bodhisattva observe any apparent arising, diminishing or destruction of the skandhas.
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Why? Because all beings and events, by their very nature are inconceivable and therefore unapproachable, ungraspable, unfindable, unrepresentable. Thus the awakened bodhisattva manifests spontaneously the transcendent insight known as not grasping any separate thing - the omniscient insight which is limitless, unwavering, sublime. This panoramic awakeness transcends even the widest vision of any contemplative practitioner who remains subtly self-conscious and self-involved.
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Even while remaining immersed in Prajnaparamita, the adamantine awareness never forms or entertains any self-conscious notion such as 'I am now deep in sublime concentration' or 'I have now entered the meditation beyond all meditations'.
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Buddha: The appearance of separately self-aware and substantially self-existing beings and events is the result of primordial ignorance which unconsciously and instinctively projects the notions of individuality, substance and separation.
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This largely unconscious reasoning blinds naive realists and even naive contemplatives to the transparent, insubstantial and yet totally functional existence of all structures and processes... They attempt to crystallize Reality temporarily or permanently into names and forms. ... They remain asleep to the pure presence, or total awakeness, which constitutes all worlds and dimensions.

Absolutely Nothing To Understand
Subhuti: Dear friends, you cannot understand, because there is absolutely nothing finite to understand. You are not lacking in refinement of intellect. There is simply nothing separate or substantial in Prajnaparamita to which intellect can be applied, because Perfect Wisdom does not present any graspable or thinkable doctrine and offers no method of contemplation.
... Those conscious beings who are mature enough to receive the radical teaching of Perfect Wisdom regard themselves simply as a display of magical power without any substantial self-existence. There should be no residual tendency to hear or grasp as some independent reality the words of the teaching, nor to isolate or reify their meaning, nor to experience as a separate reality whatever they are indicating.
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The phrases magical display, dream display, own existence and all conscious beings are simply synonymous. Every objective or subjective structure that is directly experienced as factual or palpable should be regarded as a magical display, as dream display.
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Dear divine friends, even if there could be any reality more perfect, more transcendent or more liberated than Final Nirvana, that, too, would be magical or dreamlike. The terms magical display, dream display, Buddha and Nirvana are all synonymous.

True Infinitude
Subhuti: One must remember that Prajnaparamita is inconceivably great, limitless, immeasurable and infinite simply because whatever the conventional mind separates and discriminates as material forms and conscious states are known by Prajnaparamita to be its own inconceivability, immeasurability and infinity. There is no reason to become fixated on or to extol the Perfection of Wisdom as some isolated form of greatness of perfection, because Prajnaparamita recognizes every single being, event and perception as precisely the same limitless, immeasurable, infinite perfection. This recognition is what constitutes the greatness of Perfect Wisdom.
The perfection of Prajnaparamita is infinite because it demonstrates that no one can isolate or analyze the genesis, evolution or goal of any subjective or objective process. The perfection of Prajnaparamita is infinite because it recognizes that all processes are inherently infinite and, therefore, ungraspable and unthinkable. This freedom from being perceptually and conceptually confined by the habitual mind, this opening to the limitless, immeasurability and infinite of all realms and dimensions is why Prajnaparamita is an inconceivably great perfection.
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This ungraspable purity, openness and transparency is precisely what is meant by the limitlessness, immeasurability and infinity of all beings, realms and dimensions. Recognizing this purity, openness and transparency everywhere is what constitutes the inconceivable greatness of Prajnaparamita. Rather than infinity of number or infinity of extension in space and time, this transparent depth of unthinkability is the true perfect infinitude. This alone makes Perfect Wisdom supremely perfect.

What Buddha Mind Knows
Buddha: Awakened Ones know the minds of living beings as intrinsically infinite and inexhaustible. Through all-embracing compassion, living Buddhas manifest an all-embracing mind which blissfully recognizes that just as empty space cannot disintegrate or be destroyed, neither can the infinitely open space of all minds ever be narrowed or extinguished. This inconceivably marvelous Buddha mind which knows this openness - which simply is this openness - can itself never be extinguished. Why? Because it never comes into being in the first place, and therefore possesses no duration through time that can be interrupted.
Buddha mind is the one mind of all beings - fully awakened, fully matured, fully sensitized, fully liberated.
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Tathagatas compassionately know the polluted thoughts of conscious beings precisely as they are. How? By realizing directly that the minds of those living beings who do not practice any spiritual disciplines are not actually stained by the pollution of false viewpoints. Wrong ideas possess absolutely no substantial self-existence, nor do the conventional minds in which they are claimed to lodge possess any such self-existence.
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Tathagatas kindly know that reactive thoughts react simply to their own false representations of Reality - representations which, whether subjective or objective, are empty of substantial self-existence. Tathagatas equally know nonreactive, harmonious, peaceful thoughts to be the total simplicity of Reality, never independently existing in themselves.
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Awakened Enlightenment sympathetically knows, precisely as they are, the ingrained tendencies of countless conscious beings to engage in literal affirmations and negations concerning the transparent structure of reality. Such beings - themselves constructs - take their own linguistic constructions at face value to be solidly self-existing entities. Awakened Enlightenment clearly knows that these kaleidoscopic affirmations and negations arise like a play of reflected light beams from the constituent processes of personal awareness called form, feeling, impulse, perception and consciousness. How? Because Buddha mind realizes that all possible statements have reference not to Reality but only to transparent processes and structures called personal awareness. Included in this mere kaleidoscopic play are various metaphysical statements about the Tathagata - that the Tathagata does or does not continue to exist after physical death; that the Tathagata in some sense does and in some sense does not exist after death; or that the Tathagata cannot be said either to exist or not to exist after death. None of these statements, however refined, refer directly to awakened Enlightenment - birthless as well as deathless.
Buddha mind, unveiling the inherent emptiness of self-existence, dissolves metaphysical assumptions, such as the doctrine that the self and its consciousness are eternal and that other phenomena are mere delusion. Equally inadmissible as truth are statements that the self and its consciousness are eternal, temporal, both eternal and temporal or neither eternal or temporal. It is inadmissible as well to maintain that the self and its consciousness are finite, infinite, or both or neither. Referring also to false abstractions and projections and not to Reality are doctrines which claim that the soul is confined and identical to the body or that the soul is independent from the body and from other structures of relativity.
Though the unwavering principle of Prajnaparamita, Tathagatas know all possible positive and negative assertions precisely as they are, for Buddha mind realizes the transparent processes and structures of personal and communal awareness to be simply suchness, or pure presence. Through awakening fully as pure presence, the Tathagatas know the suchness of all beings and events and of all statements about them. The whole image of phenomenal manifestation is the play of universal enlightenment through the constituents of individual and communal awareness. All is simply suchness. ... All material and mental structures manifest as one continuous presence, one absolute depth of unthinkable purity, without trace of positive or negative assertions. This pure presence is inextinguishable, indistinguishable simplicity.
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That is why the mysterious title Tathagata is conferred upon Buddhas, for Tathagata means the one who has disappeared entirely and beautifully into suchness.

Universal Principle of Inconceivability
Buddha: And why is Perfect Wisdom unthinkable? Because unthinkably profound are all points of reference: Tathagata, the disappearance into pure presence; Buddha nature, the Reality which is simply awakeness; spontaneous selflessness, the essenceless essence of all phenomena; and luminous omniscience, which knows without knower, knowing or known. Upon none of these points can thought be focused, because they are not objects or subjects. They cannot be imagined or willed, perceived or felt. They cannot be touched or approached in any way by any finite mode or procedure of consciousness.
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Can you count, compare, measure, conceive, imagine, perceive, touch or divide the principle of space?... In precisely the same manner as the principle of space are all appearances whatsoever unthinkable, unimaginable, incalibratable, unapproachable, unattainable, incomparable. For all phenomena are Buddha phenomena, arising as the open space of total awakeness, in which dividing, discriminating and discursive thought is absent, in which no comparison is feasible. ... This impossibility of any comparison is the core of the universal principle of inconceivability called Prajnaparamita.

Mirror Image of Pure Presence
Subhuti: The suchness of the Tathagata, the one who has disappeared by awakening as Reality, is the very same as the suchness of all possible structures of relativity. So the pure presence of Subhuti the Elder is universal pure presence. ... Thus it can be said that the unidentifiable Subhuti now speaking is simply indivisible, undifferentiated suchness and is therefore a living image of universal Buddha nature.
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The transparent suchness of Buddha and the transparent suchness of all phenomena are simply suchness - not divided or divisible, not multiple, not even single. This pure presence, without any second reality or subreality, is not located anywhere, nor does it come from anywhere, nor does it belong anywhere, much less is it going anywhere or evolving in any way. It is precisely because this pure presence does not belong anywhere that it is total and simple.
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At all times, and timelessly, suchness remains without substantial structure and therefore without essential description, although it appears effortlessly as Subhuti, as Shakyamuni Buddha and as all phenomena. Although there may seem to be two beings - that is, Subhuti the disciple as a separate image of Buddha, his master - nothing has been broken away from the original Buddha presence which can now be called the image of Subhuti, because pure presence remains unbroken and unbreakable.

The Diamond Sutra
The Diamond Sutra is one of the most popular scriptures in Mahayana Buddhism. In some monasteries, it is recited everyday. It is considered a distillation of the essence of the Prajnaparamita Sutras, and it belongs to that same tradition. (For an even more condensed and popular expression, see the Heart Sutra in the following section.)
Historically, the Diamond Sutra came later than the lengthy Prajnaparamita Sutras in thousands of lines, such as the one in 8,000 lines that we sampled above. That is why I am placing it here, although many Buddhists would recommend becoming familiar with this sutra before tackling the longer ones!
As a distillation of Prajnaparamita thought, the main theme of the Diamond Sutra is the central but elusive notion of emptiness. So we must once again use insight and intuition to understand the spirit of the text; a literal reading may cause confusion! Clearly, the text delights in paradox. Nevertheless, the strong similarities to what we examined above are evident, so that we are not totally lost.
The following excerpts are from the version by Plum Village, the religious center founded by the highly respected Buddhist monk, Thich Nhat Hanh. Although the translator is not credited, it is most likely Thich Nhat Hanh, who is well known for his simple, elegant and beautiful expositions of Buddhism.
The discourse of the Buddha is prompted by the following question from his disciple Subhuti:

'World-Honored One, if sons and daughters of good families want to give rise to the highest, most fulfilled, awakened mind, what should they rely on and what should they do to master their thinking?'
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The Buddha said to Subhuti, 'This is how the bodhisattva mahasattvas [aspirants to enlightenment] master their thinking. 'However many species of living beings there are - whether born from eggs, from the womb, from moisture, or spontaneously; whether they have form or do not have form; whether they have perceptions or do not have perceptions; or whether it cannot be said of them that they have perceptions or that they do not have perceptions, we must lead all these beings to the ultimate nirvana so that they can be liberated. And when this innumerable, immeasurable, infinite number of beings has become liberated, we do not, in truth, think that a single being has been liberated.'
'Why is this so? If, Subhuti, a bodhisattva holds on to the idea that a self, a person, a living being, or a life span exists, that person is not an authentic bodhisattva.'
Really this is not so illogical. No one is denying that the forms (shapes and colors) called 'people' pass across our field of vision like clouds across the sky. However, if we have no sense of self, then naturally we do not think, 'Here is a person. There is a person.' We can still interact with the world in a spontaneous and natural way, but the sense of separation and individuation so characteristic of ordinary, unenlightened consciousness has evaporated. The mystical literature of the world is unanimous that the higher state of consciousness - which Buddhists call 'enlightenment' - is characterized by a profound sense that All is One.
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'What do you think, Subhuti? Is it possible to grasp the Tathagata [Buddha] by means of bodily signs?'
'No, World-Honored One. When the Tathagata speaks of bodily signs, there are no signs being talked about.'
The Buddha said to Subhuti: 'In a place where there is something that can be distinguished by signs, in that place there is deception. If you can see the signless nature of signs, then you can see the Tathagata.'
We must lose our discriminating and individuating consciousness that always grasps for 'signs' and 'marks' ... that tries to cut reality into discrete boundaries and entities in conflict or uneasy peace with each other. Our fundamental view of the world determines our own state of consciousness. We cannot become enlightened as long as we retain our usual discriminating mind. This produces a subconscious feedback which anchors our spirit to the ground of 'common sense' and prevents it from rising to the sky of enlightenment.
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Anyone who, for only a second, gives rise to a pure and clear confidence upon hearing these words of the Tathagata, the Tathagata sees and knows that person, and he or she will attain immeasurable happiness because of this understanding. Why?
'Because that kind of person is not caught up in the idea of a self, a person, a living being, or a life span. They are not caught up in the idea of a dharma [thing] or the idea of a non-dharma. They are not caught up in the notion that this is a sign and that is not a sign. Why? If you are caught up in the idea of a dharma, you are also caught up in the ideas of a self, a person, a living being, and a life span. If you are caught up in the idea that there is no dharma, you are still caught up in the ideas of a self, a person, a living being, and a life span. That is why we should not get caught up in dharmas or in the idea that dharmas do not exist. This is the hidden meaning when the Tathagata says,'Bhiksus [monks], you should know that all of the teachings I give to you are a raft.' All teachings must be abandoned, not to mention non-teachings.'
This paragraph neatly summarizes most of what we have learned about emptiness. Another concise summary can be found in a quote from the Venerable Master Hsing Yun, who discusses the Diamond Sutra in an on-line booklet called The Diamond Sutra and the Study of Wisdom and Emptiness, available at the BLIA website:
When we speak of 'selflessness', we do not mean there is no such a person as myself. 'Selflessness' is a realm of the mind and prajna [wisdom]. It is a realm of being free from the bondage of the tangible, dualistic notion of relationship, of being able to transcend the relative concepts of self and others, and of being equal to space and the universe. There is fundamentally no differentiation of the mind, the Buddha, and sentient beings: all living beings are beings in one's mind, all the Buddhas are Buddhas in one's mind, and all things are things in one's mind. Outside of the mind, where can there be any living beings? If we think like this, then although numerous beings are freed, we do not think that a single being is freed. With such transcendental thinking, we are truly practitioners of prajna and sunyata.
Clearly, this echoes many of the ideas on this page. The Venerable Master Hsing Yun, who is based in Taiwan, is well-known for his efforts to bring 'Humanistic Buddhism' to the world. More details about Buddhism and about the master can be found at the BLIA website. (BLIA stands for Buddha's Light International Association).
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'What do you think, Subhuti, has the Tathagata arrived at the highest, most fulfilled, awakened mind? Does the Tathagata give any teaching?'
The Venerable Subhuti replied, 'As far as I have understood the Lord Buddha's teachings, there is no independently existing object of mind called the highest, most fulfilled, awakened mind, nor is there any independently existing teaching that the Tathagata gives. Why? The teachings that the Tathagata has realized and spoken of cannot be conceived of as separate, independent existences and therefore cannot be described.
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What do you think, Subhuti? Does a bodhisattva create a serene and beautiful Buddha field?'
'No, World-Honored One. Why? To create a serene and beautiful Buddha field is not in fact creating a serene and beautiful Buddha field. That is why it is called creating a serene and beautiful Buddha field.'
The Buddha said, 'So, Subhuti, all the bodhisattva mahasattvas should give rise to a pure and clear intention in this spirit. When they give rise to this intention, they should not rely on forms, sounds, smells, tastes, tactile objects, or objects of mind. They should give rise to an intention with their minds not dwelling anywhere.'
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'The Buddha said to Subhuti, 'That is quite right. If someone hears this sutra and is not terrified or afraid, he or she is rare. Why? Subhuti, what the Tathagata calls parama-paramita, the highest transcendence, is not essentially the highest transcendence, and that is why it is called the highest transcendence.
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'The Tathagata has said that all notions are not notions and that all living beings are not living beings. Subhuti, the Tathagata is one who speaks of things as they are, speaks what is true, and speaks in accord with reality. He does not speak deceptively or to please people.
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... there is, in fact, nothing that can be attained that is called the highest, most fulfilled, awakened mind. Why? Tathagata means the suchness of all things (dharmas). Someone would be mistaken to say that the Tathagata has attained the highest, most fulfilled, awakened mind since there is not any highest, most fulfilled, awakened mind to be attained. Subhuti, the highest, most fulfilled, awakened mind that the Tathagata has attained is neither graspable nor elusive. This is why the Tathagata has said, 'All dharmas are Buddhadharma.' What are called all dharmas are, in fact, not [at] all dharmas. That is why they are called all dharmas.
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'Subhuti, if you think that the Tathagata realizes the highest, most fulfilled, awakened mind and does not need to have all the marks, you are wrong. Subhuti, do not think in that way. Do not think that when one gives rise to the highest, most fulfilled, awakened mind, one needs to see all objects of mind as nonexistent, cut off from life. Please do not think in that way. One who gives rise to the highest, most fulfilled, awakened mind does not contend that all objects of mind are nonexistent and cut off from life.'
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'Subhuti, if someone were to offer an immeasurable quantity of the seven treasures to fill the worlds as infinite as space as an act of generosity, the happiness resulting from that virtuous act would not equal the happiness resulting from a son or daughter of a good family who gives rise to the awakened mind and reads, recites, accepts, and puts into practice this sutra, and explains it to others, even if only a gatha of four lines. In what spirit is this explanation given? Without being caught up in signs, just according to things as they are, without agitation. Why is this?
'All composed things are like a dream,
a phantom, a drop of dew, a flash of lightning.
That is how to meditate on them,
that is how to observe them.'
After they heard the Lord Buddha deliver this sutra, the Venerable Subhuti, the bhiksus and bhiksunis, laymen and laywomen, and gods and asuras, filled with joy and confidence, undertook to put these teachings into practice.
Those four lines of poetry are quite striking and beautiful and capture the spirit of the sutra. Shakyamuni, the human incarnation of Buddha, said that we must lose our sense of self to achieve the state of consciousness called enlightenment. The Prajnaparamita reiterates this idea while adding that of the emptiness of all things, often expressed as the dreamlike nature of what we take to be reality. These two views - the unreality of the self and of the world (dharmas) - are really mirror images of each other. Likewise, our sense that the world 'out there' is so real and solid is but the mirror reflection of our sense of our self as something solid and real that we clutch and grasp in the depth our own heart. In reality, there is one vast and pure consciousness, which we may call Buddha, which encompasses and transcends both.

The Heart Sutra

The Heart Sutra is similar to the Lord's Prayer in Christianity in that it is a brief 'statement of faith' recited constantly by Mahayana Buddhists everywhere, often before or after meditation. It is the most condensed example of the Prajnaparamita Literature, except for the famous Prajnaparamita Sutra in One Letter - which I have not been able to find in any bookstore! :) The following version is from Buddhanet, a comprehensive website on Buddhism. The link to the sutra also provides a detailed commentary by Grand Master T'an Hsu.

When the Bodhisattva Avalokitesvara
Was Coursing in the Deep Prajna Paramita
He Perceived That All Five Skandhas Are Empty.
Thus He Overcame All Ills and Suffering.

Oh, Sariputra, Form Does not Differ From the Void,
And the Void Does Not Differ From Form.
Form is Void and Void is Form;
The Same is True For Feelings,
Perceptions, Volitions and Consciousness.

Sariputra, the Characteristics of the
Voidness of All Dharmas
Are Non-Arising, Non-Ceasing, Non-Defiled,
Non-Pure, Non-Increasing, Non-Decreasing.

Therefore, in the Void There Are No Forms,
No Feelings, Perceptions, Volitions or Consciousness.

No Eye, Ear, Nose, Tongue, Body or Mind;
No Form, Sound, Smell, Taste, Touch or Mind Object;
No Realm of the Eye,
Until We Come to No realm of Consciousness.

No ignorance and Also No Ending of Ignorance,
Until We Come to No Old Age and Death and
No Ending of Old Age and Death.

Also, There is No Truth of Suffering,
Of the Cause of Suffering,
Of the Cessation of Suffering, Nor of the Path.

There is No Wisdom, and There is No Attainment Whatsoever.

Because There is Nothing to Be Attained,
The Bodhisattva Relying On Prajna Paramita Has
No Obstruction in His Mind.

Because There is No Obstruction, He Has no Fear,
And He passes Far Beyond Confused Imagination.
And Reaches Ultimate Nirvana.

The Buddhas of the Past, Present and Future,
By Relying on Prajna Paramita
Have Attained Supreme Enlightenment.

Therefore, the Prajna Paramita is the Great Magic Spell,
The Spell of Illumination, the Supreme Spell,
Which Can Truly Protect One From All Suffering Without Fail.

Therefore He Uttered the Spell of Prajnaparmita,
Saying Gate, Gate, Paragate, Parasamgate, Bodhi Svaha.

Links

Although there are many websites on Buddhism, there are few websites to date (October 2001) devoted specifically to the Prajnaparamita literature. However, the famous Heart and Diamond Sutras can be found at many Buddhist sites, as can many commentaries on these particular sutras.
Note: I do not necessarily agree with everything at the following sites, nor do I expect you to, nor do they expect us to.
Pith Instructions on the Great Perfection: Dilgo Khyentse, a kind and revered Tibetan Buddhist master, clearly discusses the essence of meditation. His description gives an insight into emptiness. This is true wisdom, which puts philosophers to shame. Another of his articles can be found here. Dilgo was the teacher of Sogyal Rinpoche who wrote the famous 'Tibetan Book of Living and Dying', which is an excellent introduction to Buddhism as well as to Tibetan experiences of the afterlife. Some of Sogyal's quotes can be found here, and excerpts from the book can be found here as well as here.
Kheper Buddhism Page: Only one section of a large and interesting website devoted to spirituality and philosophy. A link to emptiness can be found under 'Shunyata' - the Sanskrit word for emptiness. Be sure to explore the rest of this site.
Sarva Darshana Samgraha: Nanda Chandran's scholarly site devoted to Indian philosophy. Clear and not too lengthy discussions can be found of e.g. Nagarjuna. (Look for 'Madhyamika' under 'Mahayana' under 'Buddhism' under 'Heterodox Systems'.)
Realization.org This website contains of wealth of clear writings on meditation and nondualistic philosophy, with many references to related trends in Indian religion (Advaita Vedanta, Buddhism,...).
Nonduality Salon: A website devoted specifically to 'nondualistic' philosophy in all its manifestations.
Jonah Winter's Dissertation on Nagarjuna: An entire dissertation devoted to Nagarjuna and his 'Middle way' or Madhyamika.