For the good of the other, that is the answer to our question. Or is it? What does that even mean? In his Nicomachean Ethics, Aristotle explains what friendship is. Perhaps understanding friendship might help us to understand the relationship between teacher and student, even if the relationship between a teacher and his student is not one we might typically describe as a friendship.
For Aristotle, that student of Plato and therefore Socrates, there are three kinds of friendship: a friendship of utility, a friendship of pleasure, and pure friendship.
The friendship of utility is that friendship in which the other person is useful to me. He is useful in that I get something out of him, and my friendship lasts only so long as he remains useful. That usefulness can be anything: money, a pickup truck for when I need to move things, a swimming pool on hot summer days, a cabin in the woods, a deer stand for hunting. So long as I have access to the thing that makes him useful, he is useful, and we remain friends. Presumably, in a friendship of utility, I also have something useful that is available to him—unless his friendship with me is a pure friendship or a friendship of pleasure.
The friendship of pleasure is that friendship in which the other person brings me pleasure. That pleasure might be that he is entertaining, funny, a good listener, attractive. So long as I derive pleasure from his presence, we remain friends. His side of the friendship may also be one of pleasure, or it may one of utility or pure friendship.
Finally, the friendship that is pure is the friendship in which the two parties are so fond of one another, have such an affinity for one another, that they are friends not because the other is useful or pleasant, but because they want to see the other attain to the best things in life. In other words, I am a friend to the other person because I want what is good for the other person. I hope and pray for his good, and I do my part to make that happen.
Aristotle goes on to show how we can learn more about both friendship and governance by making the two ideas analogous to one another. Thus, for him, I can come to see the different kinds of friendship more clearly by comparing friendship to modes of government. The difference between a monarch and a tyrant, for example, Aristotle says is the difference between pure friendship and friendship of utility or pleasure. The monarch rules in such a way that he is trying to bring about the best for his people, their good. The tyrant rules in such a way that he is trying to get what is good for him; the people exist for his use and his pleasure.
Perhaps we can also learn more about friendship and governance and teaching if we make the three ideas analogous to one another. Does the analogy carry over to that relationship? Is there a monarchical teacher who teaches in such a way to bring about the good of his student and a tyrannical teacher who teaches in such a way to bring about only his own good? Is there a pure teacher who seeks out the student’s good and a utilitarian or pleasure-seeking teacher who sees the student as useful or pleasing? If so, what kind of teacher am I?