There is a class of speech-acts employing expressions such as ‘can't, ‘must’, and ‘meant to’, which have a paradigm role in stating the rules that govern a practice. Elizabeth Anscombe called such expressions stopping (or forcing)modals. Although “You can't phi”, etc., are not implicit hypothetical imperatives, it nevertheless makes prima facie sense to ask of a given practice why we go in for it, what the point of it is. Various questions are discussed in connection with these facts, e.g. What distinguishes a rule's applying to someone from its having force (for that person)? Where the practice at issue is a‘language-game’, does the question “Why do we do this?” still makes sense?