By definition, in a Pavlovian (classical) procedure a stimulus is presented prior to an eliciting stimulus (reinforcing stimulus) in an operant procedure a response occurs prior to the reinforcer. In spite of the different contingencies implemented by the two procedures, some behavior necessarily precedes the reinforcer in the Pavlovian procedure and some stimulus necessarily precedes the reinforcer in the operant procedure. If conditioning depends on the momentary relation of environmental and behavioral events to a reinforcer, then the two procedures must begin by engaging a common conditioning process. The cumulative effects of that common process are different, however, because of differences in the frequency with which specific environmental and behavioral events are contiguous with the reinforcer (and its elicited response). The view that the critical reinforcing event is the evocation of a change in ongoing behavior evoked by the eliciting stimulus provides the basis for an interpretation of the conditioning process that encompasses the effects of both procedures.