My aim is to question an assumption that is often made in the philosophical literature on dispositions. This is the assumption that, generally, the stimulation (or ‘triggering’) of a disposition temporally precedes the manifesting of that disposition. I will begin by examining precisely what the trigging of a disposition may be thought to consist in, and will identify two plausible views. I will then argue that on either of these views about triggering, a case can be made against the view (...) that the triggering of a disposition always occurs before the manifesting of that disposition. More precisely, if the first view about triggering is accepted, and certain plausible assumptions about dispositions are put into place, a metaphysical argument can be formulated for the claim that the stimulation of a disposition never occurs before that disposition manifests. If the second view about triggering is accepted, the question concerning simultaneity becomes an empirical one. There are, however, examples of dispositional interaction which, on the second view about triggering, clearly seem to involve simultaneity.1. (shrink)