Here’s a false generalization with manifestly false consequences: all people who differ by one millimeter in height from a short person are themselves short. Why are we inclined to believe it? Boundary-shifters, usually lumped together under the heading “contextualists”, say that we believe the false generalization because when we consider any instance, that instance is true at the time of our consideration. Critics complain that the explanation is no good, for (i) if it were, then fallacious inferences would be rampant; (ii) if it were, then we would always generalize from instances that we knew to be true at the time we considered them. But, they say, fallacious inferences are not rampant and we do not always generalize from the instances. Responses: (i) boundary-shifters require only that weakly fallacious inferences are rampant, and indeed they are; (ii) generalizing from the instances is both natural and explanatory, albeit defeasible.