The Nicomachean Ethics is Aristotle's best-known work on this subject. It consists of ten books and is based on notes from his lectures at the Lyceum. The theme of the work is the Socratic question of how men should best live. Before Socrates, philosophy was merely theoretical. This changed dramatically with Aristotle’s works, which bind philosophy to human issues. The Nicomachean Ethics are therefore practical rather than theoretical, in the original Aristotelian senses of these terms.