Having just taught Aristotle’s ethics, I want to discuss an element of his ethical theory that I find plausible but lack a satisfactory account of why it’s plausible: In contrast to the Socratic/Platonic tradition, which held that one must know the good in order to act well, Aristotle held that one must first act well — and come to so act as a matter of habit or second nature — in order to know the good. The interesting insight here (which seems obvious but is easy enough to overlook) is that one can only come to appreciate the reasons for acting in a particular way by first acting in that way. Engaging in a practice, Aristotle thought, is necessary in order to understand the point of the practice.
Now there are several concerns about this claim that I won’t pursue here (for example, how we individuate practices and whether engaging in a practice is sufficient, and not simply necessary, to understand the reasons for engaging in it), but there does seem to be some wisdom behind it. Suppose I have a friend who likes to engage in risky, daredevil-like forms of recreation (sky diving, roller coaster riding, and the like), and invites me to join him. Being jittery, I refuse his invitation. But if I had accepted, I might engage in these forms of recreation and come to perceive the value in them (that, say, there’s some exhilaration in feeling the forces of nature impinging on my body), and I couldn’t have perceived the reasons for this kind of recreation without having tried it out myself.
The crucial question to ask about Aristotle’s claim is: How is it that by engaging in a practice I come to know what’s good about that practice? Here are two obstacles I see: We might be tempted to re-analyze relevant examples so that they turn out not to be examples wherein knowledge of what’s good about a practice is what’s acquired. So we might say that all I learn in the example above is an instrumental fact, not a normative fact: I learn that risky forms of recreation serve some good that I already have knowledge and appreciation of. This would make Aristotle’s claim little more than the less interesting observation that in order to fulfill my aims, I may have to engage in activities that fulfill my aims in order to know that they fulfill my aims.  Aristotle’s claim is specific to crafts or skills, and one way in which engaging in a practice might help me value it is because engaging in it makes me better at the practice: When I first try to play the piano, I’m frustrated by how my fingers fumble across the keys, but as I improve my skills, playing becomes more enjoyable because the frustrations and challenges that confront a novice disappear. But I’m not sure if mastering the skill is a way of coming to see what’s good about engaging in the practice. Admittedly, gaining skill in a practice tilts the balance, so to speak, in that reasons I may have for not engaging in a practice (i.e., I find it difficult) diminish in force. But it seems possible to gain skill in a practice but still not see any intrinsic merit in the practice. Indeed, people often come to disdain an activity that they spent a large chunk of their lives mastering. So what more is learned about what’s good about a particular practice besides how to successfully participate in it? In other words, how does my participating in it make me see what’s worthwhile about it?
In any event, I’d be curious to know if others find the idea that one must do in order to know plausible and how it might be defended.