 Although there is no possibility of writing a book of rules, however long, that will serve as a complete guide to wise decision-making, it would be a mistake to attribute to Aristotle the opposite position, namely that every purported rule admits of exceptions, so that even a small rule-book that applies to a limited number of situations is an impossibility. He makes it clear that certain emotions (spite, shamelessness, envy) and actions (adultery, theft, murder) are always wrong, regardless of the circumstances (1107a8–12). Although he says that the names of these emotions and actions convey their wrongness, he should not be taken to mean that their wrongness derives from linguistic usage. He defends the family as a social institution against the criticisms of Plato (Politics II.3–4), and so when he says that adultery is always wrong, he is prepared to argue for his point by explaining why marriage is a valuable custom and why extra-marital intercourse undermines the relationship between husband and wife. He is not making the tautological claim that wrongful sexual activity is wrong, but the more specific and contentious point that marriages ought to be governed by a rule of strict fidelity. Similarly, when he says that murder and theft are always wrong, he does not mean that wrongful killing and taking are wrong, but that the current system of laws regarding these matters ought to be strictly enforced. So, although Aristotle holds that ethics cannot be reduced to a system of rules, however complex, he insists that some rules are inviolable.