Ethics is about conduct, not mere knowledge

Aristotle begins chapter 2 by claiming that ethics is different from other branches of philosophy because ethics is a practical discipline rather than a theoretical discipline. That is, it is concerned with doing the right thing, not just knowing the right thing. After all, one could know the right thing to do, but sit on a mountain top and do nothing, but then Aristotle would think that you aren't really living successfully.

So, says Aristotle, we need to look into our conduct: we have to ask how we are to live skillfully so as to live successfully. For as we have seen, the quality of our practice (i.e., the things we do day-in and day-out from a very young age) determines the quality of our skills.

Aristotle then brings up a principle: "to act in conformity with the right principle". This should be read like so: "be able to do the right thing at the right time, and know why you did such and thing and why it was the right thing to do at that time." Theo point here is this: doing the right thing does involve knowledge: it involves knowing what the right thing to do actually is, and knowing why it is the right thing to do. Doing the right thing, for Aristotle, is a reasoned course of action. We truly succeed at doing the right thing only when we have good reasons for doing so.

Hence, knowledge is involved here, even though ethics is a practical science. But of course, ethics also involves doing things, so it is ultimately a practical science, albeit a reasonable one.