Thomas Aquinas

“ But man can acquire universal and perfect goodness, because he can acquire beatitude. Yet he is in the last degree, according to his nature, of those to whom beatitude is possible; therefore the human soul requires many and various operations and powers. But to angels a smaller variety of powers is sufficient. In God there is no power or action beyond His own Essence.
There is yet another reason why the human soul abounds in a variety of powers---because it is on the confines of spiritual and corporeal creatures; and therefore the powers of both meet together in the soul. ”

“ The act to which primary matter is in potentiality is the substantial form. Therefore the potentiality of matter is nothing else but its essence.
Reply to Objection 3: Action belongs to the composite, as does existence; for to act belongs to what exists. Now the composite has substantial existence through the substantial form; and it operates by the power which results from the substantial form. Hence an active accidental form is to the substantial form of the agent (for instance, heat compared to the form of fire) as the power of the soul is to the soul. ”

“ But various objects which belong to various powers, belong also to some one power; as sound and color belong to sight and hearing, which are different powers, yet they come under the one power of common sense. Therefore the powers are not distinguished according to the difference of their objects. ”

“ Thus he is least of all disposed of health, who can only acquire imperfect health by means of a few remedies; better disposed is he who can acquire perfect health by means of many remedies; and better still, he who can by few remedies; best of all is he who has perfect health without any remedies. We conclude, therefore, that things which are below man acquire a certain limited goodness; and so they have a few determinate operations and powers. ”

“ Augustine is speaking of the mind as it knows and loves itself. Thus knowledge and love as referred to the soul as known and loved, are substantially or essentially in the soul, for the very substance or essence of the soul is known and loved. ”

“ For we see that the senses are for the sake of the intelligence, and not the other way about. The senses, moreover, are a certain imperfect participation of the intelligence; wherefore, according to their natural origin, they proceed from the intelligence as the imperfect from the perfect. ”

“ To make this evident, we observe that, as the Philosopher says (De Coelo ii, 12) , the lowest order of things cannot acquire perfect goodness, but they acquire a certain imperfect goodness, by few movements; and those which belong to a higher order acquire perfect goodness by many movements; and those yet higher acquire perfect goodness by few movements; and the highest perfection is found in those things which acquire perfect goodness without any movement whatever. ”

“ Further, emanation involves some sort of movement. But nothing is moved by itself, as the Philosopher proves (Phys. vii, 1,2) ; except, perhaps, by reason of a part of itself, as an animal is said to be moved by itself, because one part thereof moves and another is moved. ”