Van Valin (2013) proposed that, in sentence contexts, the two readings of verbs participating in the causative/inchoative alternation such as break (John broke the stick in half / The stick broke in half) are derived from an underspecified representation. In contrast, the active accomplishment reading of verbs such as march (The soldiers marched to the field in an hour) is assumed to be derived from the verb’s activity reading (The soldiers marched in the field for an hour). In this paper, we tested the two hypotheses in a sentence reading experiment using a priming technique. Our data are compatible with the view that verbs of the causative/ inchoative alternation are lexically underspecified: Verbs such as break yielded statistically unreliable priming for either form. However, we found no evidence for lexical derivation for verbs of the activity/active accomplishment alternation: Both forms were strongly primed and, importantly, more so than the two forms of causative/inchoative verbs.