Let’s say we take the division between subject and object as the fundamental division in an explanation of knowledge. So taken, we commit ourselves to
a.) subject and object are contraries (for they are divided against each other) and
b.) knowledge is some unity of subject and object.
The immediate problem is that knowledge seems to be a contradiction. Knowledge, on such an account, is as impossible as “hotcoldness” or “sickhealthyness” or a square circle. Contraries can’t be contrary and one. (This is the sort of problem that the Greeks picked up on quicker than we usually do.)
Aristotle responds to the dilemma by noting that there is one pair of contraries that can be one: the perfectible and the perfection; the X-able and the X. On this account, the world around us is seen as “knower-perfecting”. The eye makes the world, in addition to being “something”, be “visible”. What kind of addition is this? When we look out, do we see the world that is something, or that is visible? How do we understand the statement “this is the world that would exist, even if it were not visible”? The simplest response is to say that there would be something, even if no eyeballs ever evolved, and our experience of being in the dark gives some evidence for this. But there is no such solution when we consider the power of reason, for while we can distinguish “something” from “the visible”, “something” is itself an object of intellect. What can we divide against the “something” that the intellect knows?
Without so much explaining the division, we can at least describe the state of affairs that which corresponds to it. There is a “something” which arises from intellect and a something that is prior to it. Just as something about the world was “visible” before eyes evolved, but it was only actually visible after they did so, so too… there was something before intellect, but it was only actually something after intellect. But this can’t be so- it’s contrary to what we wanted to say. Better to say that the world is an actual something in two ways, one prio to intellect and another concomitant with intellect. This principle divides the ens rationis from ens reale.