Objection 1. It would seem that habits are not distinguished by their objects. For contraries differ in species. Now the same habit of science regards contraries: thus medicine regards the healthy and the unhealthy. Therefore habits are not distinguished by objects specifically distinct.
Objection 2. Further, different sciences are different habits. But the same scientific truth belongs to different sciences: thus both the physicist and the astronomer prove the earth to be round, as stated in Phys. ii, text. 17. Therefore habits are not distinguished by their objects.
Objection 3. Further, wherever the act is the same, the object is the same. But the same act can belong to different habits of virtue, if it be directed to different ends; thus to give money to anyone, if it be done for God's sake, is an act of charity; while, if it be done in order to pay a debt, it is an act of justice. Therefore the same object can also belong to different habits. Therefore diversity of habits does not follow diversity of objects.
On the contrary, Acts differ in species according to the diversity of their objects, as stated above (Question 18, Article 5). But habits are dispositions to acts. Therefore habits also are distinguished according to the diversity of objects.
I answer that, A habit is both a form and a habit. Hence the specific distinction of habits may be taken in the ordinary way in which forms differ specifically; or according to that mode of distinction which is proper to habits. Accordingly forms are distinguished from one another in reference to the diversity of their active principles, since every agent produces its like in species. Habits, however, imply order to something: and all things that imply order to something, are distinguished according to the distinction of the things to which they are ordained. Now a habit is a disposition implying a twofold order: viz. to nature and to an operation consequent to nature.
Accordingly habits are specifically distinct in respect of three things. First, in respect of the active principles of such dispositions; secondly, in respect of nature; thirdly, in respect of specifically different objects, as will appear from what follows.
Reply to Objection 1. In distinguishing powers, or also habits, we must consider the object not in its material but in its formal aspect, which may differ in species or even in genus. And though the distinction between specific contraries is a real distinction yet they are both known under one aspect, since one is known through the other. And consequently in so far as they concur in the one aspect of cognoscibility, they belong to one cognitive habit.
Reply to Objection 2. The physicist proves the earth to be round by one means, the astronomer by another: for the latter proves this by means of mathematics, e.g. by the shapes of eclipses, or something of the sort; while the former proves it by means of physics, e.g. by the movement of heavy bodies towards the center, and so forth. Now the whole force of a demonstration, which is "a syllogism producing science," as stated in Poster. i, text. 5, depends on the mean. And consequently various means are as so many active principles, in respect of which the habits of science are distinguished.
Reply to Objection 3. As the Philosopher says (Phys. ii, text. 89; Ethic. vii, 8), the end is, in practical matters, what the principle is in speculative matters. Consequently diversity of ends demands a diversity of virtues, even as diversity of active principles does. Moreover the ends are objects of the internal acts, with which, above all, the virtues are concerned, as is evident from what has been said (18, 6; 19, 2, ad 1; 34, 4).
Source: Summa Theologica (New Advent)