Thomas Aquinas argues that matter is informed by a rational soul to compose a human person. But a person may survive her body's death since a rational soul is able to exist and function without matter. This leads to the typical characterization of Aquinas as a dualist.

Was Aquinas a materialist?

So, given current usage, it is misleading to deny that Aquinas was a “dualist,” and extremely misleading to say that he was a “materialist.” He clearly was a kind of dualist, in the modern sense of “dualism,” and clearly was not a materialist, given the sense typically attached to “materialism.”

Is St Thomas Aquinas a dualist?

In particular, Aquinas holds that the human intellect is immaterial and that because it is, the human soul of which it is a power survives the death of the body. And that is more than enough to make him a dualist as “dualism” is generally understood today.