Theories of similarity generally agree that the simi- larity of a pair increases with its commonalities and decreases with its differences. Recent research suggests that this compar- ison process involves an alignment of structured representa- tions yielding commonalities, differences related to the com- monalities, and differences unrelated to the commonalities. One counterintuitive prediction ... [Show full abstract] of this view is that it should be easier to find the differences between pairs of similar items than to find the differences between pairs of dissimilar items. This prediction is particularly strong for differences that are related to the commonalities. We tested this prediction in two experi- ments in which subjects listed a single difference for each of a number of word pairs. The results are consistent with the pre- dictions of structural alignment. In light of these findings, we discuss the potential role of structural alignment in other cog- nitive processes that involve comparisons.