Abstract According to a criterion of difference for thoughts derived from Frege, two thoughts are different if it is at the same time possible for a rational subject to take conflicting epistemic attitudes toward them. But applying this criterion to perception-based demonstrative thoughts seems to slice thoughts too finely and lead to their proliferation, which makes the criterion implausible. I argue that such a proliferation of thoughts is blocked by transforming this criterion into a related one that is shown to be essential in individuating thoughts as they are conceived of in this paper. This has to do with the fact that what makes demonstrative sense synchronically or diachronically the same is the subject’s unreflective taking-for-granted that the object that she is perceiving is a single object that does not require her to keep track of it in the sense supposed by Evans and Campbell.