In an earlier post I quoted Empedocles:
For ’tis by Earth we see Earth, by Water Water,
By Ether Ether divine, by Fire destructive Fire,
By Love Love, and Hate by cruel Hate.
I argued in that post that the mind does have something in common with what is known, and that this common thing is the form of the thing known. However, I took for granted that Empedocles is mistaken in assuming that the thing itself must be in common in order to be known.
I did not directly say why he is mistaken. If form makes a thing what it is, and the form of a thing known is in the mind, why does the mind not become that thing? If the form of earth is in your mind, then why is your mind not literally earth?
We will naturally be inclined to say that the form in your mind is apart from its proper matter, and that you need both form and matter to make a thing. And there is nothing wrong with this answer, as far as it goes, but it seems insufficient. Suppose you have a gold coin: what is its matter? The gold coin is presumably made out of atoms of gold, and since these atoms are not in your head, you do not see gold by gold. The problem is that atoms of gold also have some form, since this is just to say there is an answer when we ask, “What is this?”, and this will be true of anything whatever that you call matter. And there is nothing to prevent you from knowing that thing as well. There is nothing to prevent you from knowing the nature of gold atoms. And thus it seems that the matter will be present, and thus there should be actual gold in your mind.
Perhaps an Aristotelian will suggest that it is prime matter that is missing. But this answer will not work, because humans have this sort of matter in common with other things. And in any case, nothing is meant by “matter” in this sense except the ability to have the form. And since the knower can have the form, they have the ability to have the form, and thus matter. So nothing is missing, and the thing known should be literally in the knower.
Thus it appears that we have a reductio. Either my account of knowledge is mistaken, or earth should actually by known by earth, which it obviously is not.
The conclusion is only apparent, however. We can resolve it by going back to what I said about form in that post and the following one. Form is a network of relationships apt to make something one. But being one not only includes internal unity, but also separation from other things. For example, suppose we now have three gold coins, instead of one: each coin is one coin, and this depends on its parts being together, rather than in a loose heap of gold dust. But the fact that the coins are three depends on their separation from one another, and thus also the fact that each coin is “one” depends on that separation.
In other words, the form of a thing includes not only internal relationships, but also external relationships. This implies that to know the nature of a thing, one must know its external relationships. And to know a thing perfectly would require knowing both its internal and external relationships perfectly.
Now one of the things to which it is related is the very one who knows it. Thus, if the knower is to know the thing perfectly, they must perfectly understand the relationships between themselves and the thing. But this is not possible, for reasons explained in the post on self-reference. The person who attempts to know something perfectly is in the situation of someone attempting to draw a picture of themselves drawing a picture: to make a perfect copy of the gold coin, it is necessary to copy its context, which includes the knower. But this cannot be done; therefore perfect knowledge of the coin is impossible.
A different way to state the same analysis: “perfect copy” is a contradiction in terms, because such perfection would imply identity with the original, and thus not being a copy at all. In other words, perfect knowledge of a thing is impossible because perfect knowledge would imply, as in the argument of Empedocles, that one’s knowledge would literally be the thing known, and thus not knowledge at all.