The unmoved movers are, themselves, immaterial substance, (separate and individual beings), having neither parts nor magnitude.

In itself, the soul is an immaterial substance.

Schopenhauer wrote that "the assumption was made of a second substance, outside and along with matter, namely an immaterial substance."

Whether, the same immaterial substance remaining, there can be two persons.

I agree, the more probable opinion is, that this consciousness is annexed to, and the affection of, one individual immaterial substance.

And he felt an unnameable, immaterial substance meet and give way before the falling staff.

Specifically, we do not know that minds are immaterial substances whose nature does not go beyond those properties we think are essential to them.

We do not know, for instance, whether thought might not have a purely material basis, instead of being the unexplained property of an immaterial substance.

Similarly, the identity of a person does not depend on the continuity of an immaterial substance, a mind or soul.

If there are no material substances, then it must be an immaterial substance.