Introductory Note: By a very long tradition, philosophy is said to involve three things: physics (i.e., the philosophical study of natural order), logic (i.e., the philosophical study of rational order), and ethics (i.e., the philosophical study of human order). Each of these aspects of philosophy has a unifying principle or 'springboard', a concept that serves as a platform from which you can reach anything else. For physics, the springboard is change, for logic the springboard is sign, and for ethics the springboard is habitude. Habitude (Gk. hexis, Lat. habitus, often transliterated into Eng. as 'habit') is arguably understudied, so I thought I would here and there translate some texts of Aquinas on the topic.
Therefore he [Aristotle] says, first, that for investigating what is virtue, one must assume three things in the soul, namely, passions, powers, and habitudes, one of which it is necessary for virtue to be. Thus he said above that virtue is a principle of certain works in the soul; but nothing is in the soul as a principle of working unless it is one of these three. For it seems that man sometimes acts from passion, such as anger, sometimes from habitude, such as when he works from productive skill, sometimes from bare power, as when he first begins to work. And it is clear that under this division is not comprehended absolutely everything that is in the soul, because the essence of the soul is not any of these, nor is even intelligible working; rather, only those things are touched on that are principles of some action.
Then when he says, "But I call passions" &c., he explains [manifestat] the members of the previous division. And first he explains those that are passions, second those that are powers, at "And powers" &c., and third those that are habitudes, at "Habitudes according to which" &c....
Then, at "Habitudes according to which" &c., he explains those that are habitudes. And this is not done in general, but in moral matters through comparison to the passions. And he says that habitudes are called such according as we have passions well or badly. For a habitude is a kind of disposition determining a power through comparison to something, which determination, if it is appropriate to the nature of the thing, will be a good habitude disposing one to doing something well, and otherwise it will be a bad habitude so that according to it something will be done badly. And he gives the example [exemplificat] that according to some habitude we have it in us to be angry either badly, when this is done either vehemently or lackingly, that is according to excess or defect, or well, when this is done in the manner of the mean.
[Thomas Aquinas, Commentary on the Nicomachean Ethics, lecture 5, sections 290, 291, & 298, my translation. Even at the cost of some occasional awkwardness, I have attempted to clearly distinguish opere words for action from agere words for action, by using 'work'-related words for the former.]
