Abstraction from matter is too often sullied by the idea of extraction- that there should be a lump over here we know, and a lump over there we leave aside.It is better to imagine form as essentially communicative in two directions: it commuicates itself to matter by producing an existent material thing, it communicates itself to mind by producing knowledge of that same thing. Form mediates the double total emptiness of matter on the one hand, and the human mind on the other. It communicates to them one and the same existence, but the existence is not had in the same way.
But if the existence is not had in the same way, how can we know the thing? Do we not necessarily know it differently than it is? Here we see a crucial first premise in knowledge: truth does not require that the way we know things be the same as the way they exist. This is clear even from sensation. One and the saem roundness, or number, or change can be known by many senses. One existence is known in different ways by different senses.