The conventionalization of figurative comparisons is one source of lexical evolution. For example, anchor once only meant a device for mooring a ship, but may now be used to describe any source of stability or confidence. Our goal is to understand this process. Following the Career of Metaphor framework, figurative mappings are interpreted through a structure-mapping process, rendering common structure salient. As figurative terms become conventionalized, (1) the figurative sense becomes associated with the base term; and (2) there is shift from simile form to metaphor form. In two studies we investigated psycholinguistic properties that may influence this process: relationality and aptness. We use relative preference for the metaphor form as an estimate of degree of conventionalization; by determining the preferred form for a set of figuratives, we find evidence that both aptness and relationality influence this process. We speculate that figurative comparisons may give rise to new relational terms.