For purpose and virtue of humans, you might wish to read this as a significant representation of 13th century thought, and in particular:
" When Aristotle sought to isolate the human good, he employed the so-called function argument. If one knows what a carpenter is or does he has the criteria for recognizing a good carpenter. So too with bank-tellers, golfers, brain surgeons and locksmiths. If then man as such has a function, we will have a basis for deciding whether someone is a good human being. But what could this function be? Just as we do not appraise carpenters on the basis of their golf game or golfers on the basis of their being able to pick locks, we will not want to appraise the human agent on an incidental basis. So too we do not appraise the carpenter in terms of his weight, the condition of his lungs, or his taste buds. No more would we appraise a human being on the basis of activities similar to those engaged in by non-human animals. The activity that sets the human agent apart from all others is rational activity. The human agent acts knowingly-willingly. If this is the human function, the human being who performs it well will be a good person and be happy.
Thomas argues that there is one single end for all human beings, and that it is happiness. However, that is a formal description of the end, leaving open the material specification of just what that happiness is for a human being. Thomas distinguishes in the Summa Theologiae between the imperfect happiness of this life and the perfect happiness of the next life in beatitude or union with God. And on the basis of this distinction some will argue that Aquinas ultimately finds Aristotle's function argument unsatisfying, insofar as the result of the function argument is supposed to be the claim that happiness consists in a complete life lived in accord with reason and virtue. And here again it will be claimed that Aquinas in some sense rejects the fundamentals of the Aristotelian account. Insofar as he describes the life in accord with reason and virtue in this life as imperfect, he must be suggesting that it is in some sense faulty, not true or real happiness. Real happiness is something other. "
Once a magus is there, he will also understand that magic improvement is typically 'sideways', and easiest by taking examples from non-human beings.