Although not all philosophy is the same, the dominant thrust of philosophy in the last two hundred years has been a search for logically certain knowledge: for truths that we can be sure of in the same way we are sure of the proven truths of mathematics.
Science also depends on logical and mathematical reasoning, but it balances pure thought with experiment. The truths of science are tested to see if they are also "true" in the natural world, as well as in the realm of reason. Buddhism has elements of philosophy and of science, but it does not aim to discover either logical or empirical ("real world") "truths."
The aim of Buddhism is liberation: to change the way we experience ourselves and the world. Buddhism respects logical and empirical "facts," but Buddha was not interested in knowledge for its own sake. To rely on objective truth is to be like a man who has been shot by a poisoned arrow but who refuses to have it removed (and save his life) unless he first knows who shot the arrow, where his family came from, what kind of poison he used, etc. The endless real world facts surrounding his circumstances are interesting, perhaps even fascinating from an historical and scientific point of view, but only removing the arrow will save his life.
So, when we discuss the human mind, and the nature of our experience, philosophy, science, and analysis based on meditation and religious experience (Buddhism) often cover the same ground, using similar words, but the "truth" they are aiming at is slightly different in each case.
A Buddhist description of the workings of our mind varies somewhat over the millennia because the systems of thought which are used to help us gain liberation are "skillful means," rather than absolute philosophical truths, or scientific theories to be tested experimentally. As one ancient teacher put it, if the methods didn't change from time to time, the weeds would be growing ten feet high outside the temple!
Nevertheless, there is a great deal of continuity in Buddhist thought over the centuries because all the systems are attempts to describe the experience of enlightenment, and the methods for achieving it. Buddhism is always talking about the world as experience. It does not attempt, as science does, to describe the world as it exists on its own, "objectively" as we say.
When Gunabhadra, the teacher of Bodhidharma (the "founder" of Zen), is quoted as saying, "The leaves of a tree can preach the Dharma....A pillar can preach the Dharma....Earth, wood, tile, and stone can also preach the Dharma," he is not laying out logical truths or the results of his experiments. Nor is he crazy and "hearing things." He is simply reporting his non-dual experience of the world: everywhere he looks there is only oneness.
When Joshu was asked, "What is the meaning of the Patriarch's [Bodhidharma's] coming from the West?" he answered, "The oak tree in the front garden." He replies with a "weather report" from the world of enlightenment at that moment. There is nothing "dark" or "mystical" going on here; the "everyday mind" is Buddha. But, he does not say, "Look at that tree," or "I see an oak," or "Coming from the West means...," or "Enlightenment is like that oak," etc. Those statements all assume that we are "here" and the oak is "there." In other words, they reveal our usual experience of a world in which there are "subjects" (ourselves as witnesses) and "objects" (the oak as witnessed).
Dogen uses a similar device in his famous re-writing of a dualistic, philosophical statement from the Mahaparinirvana Sutra, "All sentient beings have buddha nature." This is perfectly correct from our usual standpoint where we separate our world into objects, and persons, and the qualities they possess. Dogen's version of the quote is, "All sentient beings, all things, are buddha nature." Buddha nature is not something we possess, it's what we are! Mind is everywhere. This is the world as experienced by the enlightened mind, not the world described by the poet or philosopher, or weighed and measured by the scientist.
In the same way, the Soto school insists on the non-duality of practice and enlightenment. Only our ignorance makes us think we are separated from our Buddha Nature. Sitting in meditation is enlightenment. Our job is to see that, just as Dogen did.