"Beneficial effects on legislative behavior that will result if "judges" or "courts" adopt a particular approach to interpretation. In this paper I claim that such arguments are conceptually confused, and thus do not count as valid arguments at all. Dynamic arguments commit the fundamental mistake of overlooking the collective character of judicial institutions - of overlooking that the judiciary, like Congress, is a "they," not an "it." That mistake produces the critical, and erroneous, assumption that coordinated judicial adoption of some particular approach to legal interpretation is both feasible and desirable. That assumption commits two logical fallacies simultaneously. The fallacy of division arises when a claim that is true of, or justified for, a whole set is taken to apply to any particular member of the set. The fallacy of composition arises when a claim that is true of, or justified for, any particular member of a set is taken to apply to the whole set. Both fallacies infect dynamic interpretive arguments. First, the claim that a given approach would be best for the whole court or judiciary does not entail that it would be best for any given judge taken alone. The inference from the group-level claim to the individual-level claim fails if judicial coordination on a particular approach is infeasible or unlikely. Second, the claim that a particular approach is best for any given judge need not entail that it would be best for the whole court (or judiciary). If a diversity of approaches is desirable for systemic and institutional reasons, then it would be an affirmative bad for all judges to coordinate on a particular approach. To overlook the first point is to commit the division fallacy; to overlook the second is to commit the composition fallacy. The same reasoning applies from the standpoint of every judge in the system."