When ideas are formed in this way, a variety of things happen presumably also in what is described as the sphere of consciousness and regarded as pertaining to the soul. But does the tree stand "in our consciousness," or does it stand on the meadow? Does the meadow lie in the soul, as experience, or is it spread out there on earth? Is the earth in our head? Or do we stand on the earth?
It will be said in rebuttal : What is the use of such questions concerning a state of affairs which everybody will in fairness admit immediately, since it is clear as day to all the world that we are standing on the earth and, in our example, face-to-face with a tree? But let us not slip too hastily into this admission, let us not accept and take this "clear as day" too lightly. For we shall forfeit everything before we know it, once the sciences of physics, physiology, and psychology, not to forget scientific philosophy, display the panoply of their documents and proofs, to explain to us that what we see and accept is properly not a tree but in reality a void, thinly sprinkled with electric charges here and there that race hither and yon at enormous speeds. It will not do to admit, just for the scientifically unguarded moments, so to speak, that, naturally, we are standing face to face with a tree in bloom, only to affirm the very next moment as equally obvious that this view, naturally, typifies only the naïve, because pre-scientific, comprehension of things. For with that affirmation we have conceded something whose consequences we have hardly considered, and that is: that those sciences do in fact decide what of the tree in bloom may or may not be considered valid reality. Whence do the sciences which necessarily are always in the dark about the origin of their own nature derive the authority to pronounce such verdicts? Whence do the sciences derive the right to decide what man's place is, and to offer themselves as the standard that justifies such decisions? And they will do so just as soon as we tolerate, if only by our silence, that our standing face-to-face with the tree is no more than a pre-seientifically intended relation to something we still happen to call "tree." In truth, we are today rather inclined to favor a supposedly superior physical and physiological knowledge, and to drop the blooming tree.
When we think through what this is, that a tree in bloom presents itself to us so that we can come and stand face-to-face with it, the thing that matters first and foremost, and finally, is not to drop the tree in bloom, but for once let it stand where it stands. Why do we say "finally"? Because to this day, thought has never let the tree stand where it stands.
Still, the scientific study of the history of Western thought reports that Aristotle, judged by his theory of knowledge, was a realist. A realist is a man who affirms the existence and knowability of the external world. Indeed, it never occurred to Aristotle to deny the existence of the external world. Nor did it ever occur to Plato, any more than to Heraclitus or Parmenides. But neither did these thinkers ever specifically affirm the presence of the external world, let alone prove it.