A strong case can especially be made for saying that Aristotle was a materialist about sense perception, in which an organ of perception undergoes change by being affected from without.

Was Aristotle an idealist or materialist?

However, as revealed in his psychological works, Aristotle is no reductive materialist. Instead, he thinks of the body as the matter, and the psyche as the form of each living animal.

Was Aristotle a dualist?

Belief in the possibility of the soul's existence separately from the body suffices to make one a dualist, but Aristotle rejects that belief for at least most types of soul. If Aristotle is committed to dualism, he must be committed to a weaker version of it which admits that the soul cannot exist apart from the body.