Rips and Conrad (1989) found a kind-part reciprocal effect in models of the mind, in that one mental activity is part of another if the second is a kind of the first, and vice versa. In the present paper, we hypothesize that a formally analogous effect occurs at the level of activity instances. In particular, we hypothesize that an act is judged to be an instance of an act category referred to by an activity verb if the activity is judged to be an important part of the act, and vice versa. Empirical support for this hypothesis is found in three studies with activity verbs. The converse part-instance relation is further noted to parallel the part-instance association for a specific type of metonymically defined categories. Rips and Conrad's kind-part reciprocal effect is shown to be a logical consequence of the converse part-instance relation.