If, however, we speak of those habits that are dispositions to operation, and belong properly to the powers; thus, again, there may be several habits in one power.  The reason for this is that the subject of a habit is a passive power, as stated above (Q. 51, A. 2):  for it is only an active power that cannot be the subject of a habit, as was clearly shown above (Q. 51, A. 2).  Now a passive power is compared to the determinate act of any species, as matter to form:  because, just as matter is determinate to one form by one agent, so, too, is a passive power determined by the nature of one active object to an act specifically one.  Wherefore, just as several objects can move one passive power, so can one passive power be the subject of several acts or perfections specifically diverse.  Now habits are qualities or forms adhering to a power, and inclining that power to acts of a determinate species.  Consequently several habits, even as several specifically different acts, can belong to one power.

Reply Obj. 1:  Even as in natural things, diversity of species is according to the form, and diversity of genus, according to matter, as stated in Metaph. v, text. 33 (since things that differ in matter belong to different genera):  so, too, generic diversity of objects entails a difference of powers (wherefore the Philosopher says in Ethic. vi, 1, that “those objects that differ generically belong to different departments of the soul"); while specific difference of objects entails a specific difference of acts, and consequently of habits also.  Now things that differ in genus differ in species, but not vice versa.  Wherefore the acts and habits of different powers differ in species:  but it does not follow that different habits are in different powers, for several can be in one power.  And even as several genera may be included in one genus, and several species be contained in one species; so does it happen that there are several species of habits and powers.

Reply Obj. 2:  Although a power is simple as to its essence, it is multiple virtually, inasmuch as it extends to many specifically different acts.  Consequently there is nothing to prevent many superficially different habits from being in one power.

Reply Obj. 3:  A body is informed by its shape as by its own terminal boundaries:  whereas a habit is not the terminal boundary of a power, but the disposition of a power to an act as to its ultimate term.  Consequently one same power cannot have several acts at the same time, except in so far as perchance one act is comprised in another; just as neither can a body have several shapes, save in so far as one shape enters into another, as a three-sided in a four-sided figure.  For the intellect cannot understand several things at the same time actually; and yet it can know several things at the same time habitually. ________________________

SECOND ARTICLE [I-II, Q. 54, Art. 2]