Summa contra Gentiles2.97 Chapter XCVII. That the intellect of a separate substance always understands actually

From the foregoing it is also clear that the intellect of a separate substance always understands actually.

For that which is sometimes in act and sometimes in potentiality, is measured by time. But the intellect of a separate substance transcends time, as we have proved. Therefore it is not sometimes actually understanding and sometimes not.

Moreover. Every living substance exercises actually some operation by virtue of its nature, although other operations are in it potentially: thus animals are always in the process of nourishment, although they do not always sense. Now, separate substances are living substances, as is clear from what has been said. Therefore by their nature they must needs be always actually understanding.

Again. The separate substances, according to the teaching of philosophers, move the heavenly bodies by their intellect. Now the movement of the heavenly bodies is always continuous. Therefore the understanding of separate substances is continuous and perpetual.

The same conclusion follows even if we deny that they move the heavenly bodies, since they are higher than the heavenly bodies. Wherefore, if the proper operation of a heavenly body, which is its movement, is continuous, much more will the proper operation of separate substances, namely understanding, be continuous.

Moreover. Whatever sometimes operates and sometimes does not operate, is moved either per se or accidentally. Wherefore the fact that we are sometimes understanding and sometimes not understanding, is due to an alteration in the sensible faculty, as stated in 7 Phys. But separate substances are not moved per se, since they are not bodies; nor are they moved accidentally, since they are not united to bodies. Therefore their proper operation, which is to understand, is continual in them without any interruption.