Our account of this science will be adequate if it achieves such clarity as the subject-matter allows; for the same degree of precision is not to be expected in all discussions, any more than in all products of handicraft.
This statement, which appears in Book I, Chapter 3, is the first of a number of caveats with which Aristotle warns us not to expect any precise rules or codes of conduct. This is not laziness on Aristotle’s part, but, as he explains, the nature of the beast. Ethics deals with the vagaries of human life and must remain flexible enough to account for the great deal of variety and possibility.
Furthermore, Aristotle tells us that virtue cannot be taught in a classroom but can be learned only through constant practice until it becomes habitual. If virtue consisted of hard and fast rules, it would indeed be possible to lay them out explicitly in a classroom. Unfortunately for those hoping for the easy road to success, no such rules exist. Knowing what to do is a matter of applying phronesis, or prudence, on a case-by-case basis.