Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 17; q. 9, a. 2, ad 3.

109. Command properly is an act of practical reason: for it is an expression of the will by which the work to be done is intimated to someone (do this), and a ordering necessitating the one commanded to do the work; but to express and to order belong to reason, not to the will. — Nevertheless, the will is said to command the other powers whose acts are called commanded: a) by taking to command improperly for to move, because the will moves the other faculties to exercise and to the end; b) also properly: because, since the choice of the will moves reason to command, therefore command has from the will its force and efficacy of moving the other powers; but the act is rather to be attributed to the moving power than to the moved power (e.g., killing is more attributed to the will than to the hand); whence command is rather attributed to the will than to the intellect.

110. Command and the commanded act are one human act. — For command and the act commanded by it itself are said to have order to one another; and therefore, although physically they are several, morally, however, they are simply one and the same human act, like a certain one whole: in which the commanding mover holds itself as the formal element, the commanded act is had materially; — yet they are several according to parts.

111. Those acts can be commanded which are in our domain or power, and toward which a persuasive reason can move us; namely: 1° acts of the will, which are maximally in our power and over which the intellect, just as it can judge, so too can command: for by one act the will can move itself to another, insofar as it moves reason to propose or command this; in which case that act will be at once elicited by the will and commanded by it. The first act of the will is excepted, to which a man does not move himself by another act, but is moved by God alone; 2° acts of reason, not as regards the perception of the object, nor as regards assent or adherence to such or such an object, unless the matter concerns non-evident things; — but as regards the exercise or application: for the will moves reason to act, and reason reflects upon its own acts and so can dispose of its acts, — except the first act of reason, which precedes every act of the will and does not depend on it, except as regards its continuation; 3° acts of the sensitive life, as regards exercise and application, not indeed as dependent on the disposition of the body, but insofar as they depend on the sensitive power and on imagination, and do not anticipate reason and will but follow them; 4° acts of the external senses and members which are moved by the sensitive powers, such as the eye, hand, foot, tongue. On the contrary cannot be commanded: a) the first act of reason and of the will; b) acts of the sensitive powers anticipating reason; c) acts of the vegetative life which follow natural appetite; d) acts of the external members which are moved by a natural power, such as the movement of the heart and of the genital member; unless sometimes indirectly, insofar as by the influence of the nervous system and the sensitive part an acceleration can occur in the circulation of the blood and thus a commotion of the heart or of the genital organ. 112. The dominion of the will over the other powers can be perfect or despotic (such as is the dominion of a master over a slave) when it is not resisted: in such a way it moves itself, and through itself the locomotive power, the external senses, and the other exterior members; — but, after original sin, it is often imperfect or political (such as is the dominion of a king over free men), which is sometimes resisted or not obeyed: in such a way it moves the intellect, the internal senses, and the sensitive appetite: for thoughts or passions rise up against the will, nor do they always follow if they are chosen and excited by the will.