 On the other hand, the mode or determination of the subject, in regard to the nature of the thing, belongs to the first species of quality, which is habit and disposition: for the Philosopher says (Phys. vii, text. 17), when speaking of habits of the soul and of the body, that they are “dispositions of the perfect to the best; and by perfect I mean that which is disposed in accordance with its nature.” And since the form itself and the nature of a thing is the end and the cause why a thing is made (Phys. ii, text. 25), therefore in the first species we consider both evil and good, and also changeableness, whether easy or difficult; inasmuch as a certain nature is the end of generation and movement. (Aquinas, Summa Theologica, Part I-II, Q. 49, Art. 2)