In Aristotles logic (organon) he says:
If I say that Socrates is a man, I have said what Socrates is, and signified a substance (ousia)
There is some ambiguity here: Is he saying that Socrates is a substance, or the genus man is?
He distinguishes between primary and secondary substances; and it appears that, for example, the genus man is a secondary substance; this would suggest that Socrates is a primary substance; but he writes:
A substance, that which is called a substance most strictly, primarily, and most of all - is that which is neither said of a subject, nor in a subject. I've the individual man or individual horse.
How can Socrates be a primary substance, but at the same time it can't be in him, nor said of him?