Proposes that in understanding a metaphor, an individual sees a concept from one class or domain in terms of its similarity, in 2 aspects, to a concept from another class or domain. The 2 aspects of similarity are within-domain similarity (the degree to which 2 concepts occupy similar positions in their own class or domain) and between-domain similarity (the degree to which the classes or domains occupied by the concepts are themselves similar). Results from 2 experiments with 97 Ss indicate that aptness of metaphors related positively to between-domain distance, negatively to within-domain distance, and not at all to overall distance. Metaphors are thus perceived as more apt to the extent that their terms occupy similar positions within domains that are not very similar to each other. Results also show that the rank of an alternative's within-domain distance correlated with its relative popularity. (35 ref) (PsycINFO Database Record (c) 2007 APA, all rights reserved)