This chapter discusses reductive explanation, normative constraints, 'rule' as a metaphor, implicit norms and explicit rules, following a rule versus acting in accordance with a rule, causes and contingencies in rule-following, the paradox of interpretation, dispositions, authority of rules and justification, agreement, 'grammar' and its autonomy. By exploring the ways the concept of 'rule' is used in relation to human social regularities, Wittgenstein shows that reductions of such regularities to the output of causal mechanisms are misguided. Wittgenstein's conception of human life and how the psychology of human action should be studied is built on relations to rules and how people understand them. By teaching a rule people are not inducing a mental state common to all those who have learned the skill employed in skillfully exhibiting knowledge of the rule. Wittgenstein generalizes the concept of grammar to include all the rules, explicit or implicit, that are relevant to a practice.