Psychological state verbs pose problems for theories of the syntax-semantics interface as they can appear with either the stimulus as the subject and the experiencer as the object (SS verbs, e.g. frighten), or vice versa (SO verbs, e.g. fear). In semantic bootstrapping proposals, one of these mapping is treated as an innate default. However theorists disagree about which is the canonical mapping (compare Pinker, 1984 with Grimshaw, 1990) and diary studies suggest the two emerge simultaneously in development (Bowerman, 1990). In Experiment 1, adults, 4- and 5-year-olds showed a trend towards better comprehension of SS-verbs (p=.06), with 4-year-olds performing at chance on SO-verbs. In a less taxing Experiment 2, 4-year-olds again exhibited superior comprehension of SS-verbs (p<.01), misanalyzing two SO-verbs as SS-verbs. Curiously, SO-verbs are more common in child-directed speech. We conclude that the SS mapping is acquired more easily and discuss implications for theories of argument realization.