The ancients, however, not properly realizing the force of intelligence, and failing to make a proper distinction between sense and intellect, thought that nothing existed in the world but what could be apprehended by sense and imagination. And because bodies alone fall under imagination, they supposed that no being existed except bodies, as the Philosopher observes (Phys. iv, text 52,57). Thence came the error of the Sadducees, who said there was no spirit (Acts 23:8).
But the very fact that intellect is above sense is a reasonable proof that there are some incorporeal things comprehensible by the intellect alone.
Reply Obj. 1: Incorporeal substances rank between God and corporeal creatures. Now the medium compared to one extreme appears to be the other extreme, as what is tepid compared to heat seems to be cold; and thus it is said that angels, compared to God, are material and corporeal, not, however, as if anything corporeal existed in them.
Reply Obj. 2: Movement is there taken in the sense in which it is applied to intelligence and will. Therefore an angel is called an ever mobile substance, because he is ever actually intelligent, and not as if he were sometimes actually and sometimes potentially, as we are. Hence it is clear that the objection rests on an equivocation.
Reply Obj. 3: To be circumscribed by local limits belongs to bodies only; whereas to be circumscribed by essential limits belongs to all creatures, both corporeal and spiritual. Hence Ambrose says (De Spir. Sanct. i, 7) that "although some things are not contained in corporeal place, still they are none the less circumscribed by their substance." _______________________
SECOND ARTICLE [I, Q. 50, Art. 2]
Whether an Angel Is Composed of Matter and Form?
Objection 1: It would seem that an angel is composed of matter and form. For everything which is contained under any genus is composed of the genus, and of the difference which added to the genus makes the species. But the genus comes from the matter, and the difference from the form (Metaph. xiii, text 6). Therefore everything which is in a genus is composed of matter and form. But an angel is in the genus of substance. Therefore he is composed of matter and form.
Obj. 2: Further, wherever the properties of matter exist, there is matter. Now the properties of matter are to receive and to substand; whence Boethius says (De Trin.) that "a simple form cannot be a subject": and the above properties are found in the angel. Therefore an angel is composed of matter and form.
Obj. 3: Further, form is act. So what is form only is pure act. But an angel is not pure act, for this belongs to God alone. Therefore an angel is not form only, but has a form in matter.