What does immaterial mean for Aristotle?

Question

Many old definitions of material and immaterial leave something to be desired.

For example, how does a (supposedly) sizeless electron fit into Descartes' world of res extensae and res cogitantes?

A more modern approach is to use the term physical. A photon is sizeless and even massless (no rest mass), but it is physical, because it can be observed. The debate in modern philosophy is then if "stuff" like qualia may be non-physical.

Now, from my understanding of Aristotle, he didn't have a concept of qualia and regarded the whole "sensing something" as a completely material process.

Yet he argued that the intellect is immaterial...

So, what is it that makes matter matter for Aristotle? What is his definition of material and immaterial?

It seems that matter for Aristotle encompasses everything physical (in the modern understanding) and even more.

Answer 1

how does a (supposedly) sizeless electron fit into Descartes' world of res extensae and res cogitantes?

Does it?

A more modern approach is to use the term physical.

As far as I know, Aristotle invented the word τὰ ϕυσικά (lit. "natural things"), which is the collective title of his physical treatises. Natura comes from natio = birth, so natural things are generated, the product of a change.

A photon is sizeless and even massless (no rest mass), but it is physical, because it[s effects] can be observed. The debate in modern philosophy is then if "stuff" like qualia may be non-physical.

That seems to be a rehashing of the age-old "problem of universals."

Now, from my understanding of Aristotle, he didn't have a concept of qualia and regarded the whole "sensing something" as a completely material process. Yet he argued that the intellect is immaterial...

Aristotle is not an empiricist; he doesn't think knowledge begins and ends in the senses but begins with the senses and ends in the intellect. He argued that we are conceived as blank slates only to gain knowledge through the senses with life experience. (cf. his De sensu et sensato)

So, what is it that makes matter matter for Aristotle? What is his definition of material and immaterial?

Matter is that which is in potentiality, something that can be but is now not. (cf. St. Thomas Aquinas's short work De Principiis Naturæ, which summarizes Aristotle's Physics)

It seems that matter for Aristotle encompasses everything physical (in the modern understanding) and even more.

cf. my question on whether material or changeable beings (ens mobile) are the same as sensible beings (ens sensibile)