To the second one proceeds thus. It seems that no habitude is able to be caused by act. For a habitude is a sort of quality, as was said above. But every quality is caused in some subject inasmuch as it is receptive of something. Therefore since what acts does not receive something, but rather sends forth from itself, it seems that there is not able to be a habitude generated from act in an agent.
Further, that in which some quality is caused, is moved to that quality, as is obvious in a cooled or heated thing, but what produces the act causing the quality, moves, as is obvious with cooling and heating. Therefore if habitude were caused in something by its own act, it would follow that mover and moved, agent and patient, would be the same, which is impossible, as is said in Physic. VII.
Further, an effect is not able to be nobler than its cause. But habitude is nobler than act preceding habitude, which is obvious from this, that it renders act nobler. Therefore habitude is not able to be cause by an act preceding the habitude.
But contrariwise, the Philosopher in Ethic. II teaches that habitudes of virtues and vices are caused by acts.
I reply that it must be said that in an agent there is sometimes only the active principle of its act, as in fire there is only the active principle of heating. And in such an agent there is not able to be any habitude cause by its own act, and thus it is that natural things are not able to be accustoming or unaccustoming [consuescere vel dissuescere], as is said in Ethic. II. But some agent is found in which there is the active and passive principle of its act, as is obvious in human acts. For the acts of appetitive virtue proceed from the appetitive impulse [vi appetitiva] according as it is moved by the apprehensive impulse [vi apprehensiva] representing the object, and beyond this, the intellectual impulse [vis intellectiva], according as it reasons about conclusions has as its active principle a proposition known through itself [per se notam]. Thus from such acts habitudes are able to be caused in the agent, not indeed with respect to the first active principle, but with regard to the principle of the act that moves the moved. For everything that is endured and moved from another is disposed through the act of an agent; thus from multiplied acts there is generated a sort of quality in passive and moved power, which is called habitude; just as the habitudes of the moral virtues are caused in appetitive powers, inasmuch as they are moved by reason, and the habitudes of kinds of knowledge [scientiarum] are caused in the intellect, inasmuch as they are moved by first propositions.
Therefore to the first it must be said that the agent, inasmuch as it is agent, does not receivng something. But inasmuch as it acts as moved by another, it receives something from the mover, and so habitude is caused.
To the second it must be said that the same, according as it is same, is not able to be mover and moved. But nothing prevents the same being moved by itself according to diverse things, as is proved in Physic. VIII.
To the third it must be said that the act proceeding habitude, inasmuch as it proceeds from active principle, proceeds from a nobler principle than the generated habitude, just as reason itself is a nobler principle than the habitudes of moral virtues generated in appetitive impulse [vi appetitiva] by customary acts; and understanding of principles is a nobler principle than knowledge of conclusions [scientia conclusionum].
[Thomas Aquinas, ST 2-1.51.2, my translation; the Latin is here, the Dominican Fathers translation is here.]
This, of course, gives us habitudes that are not natural in the sense that the previous article considered. It's easy to overlook, but this article is also an indirect discussion of free will and rational learning, which involve acts that cause habitudes.
