A literal base theory of figurative language holds that figurative claims are modeled on literal forms of expression. They use surface features of literal forms but relax their constraints. We test this theory on metaphors ("Rumors are weeds") and similes ("Rumors are like weeds"), which have forms of literal categorization and similarity claims, respectively. Consistent with the literal base theory, we report the metaphor form is preferred over the simile form when the similarity between the topic (rumors) and the vehicle (weeds) is quite high. Indeed, similarity was found to be more important than familiarity, another potential factor that might affect preference for one form or the other. Our explanation is that in literal language, the categorical form ("That is an apple") is used when there many common properties, whereas the similarity form ("That is like an apple") is used when there are few common properties.