The main purpose of this paper is to show that all types of psychological interactions may be understood as matters of substitution of functions or function transfer. On the basis of this analysis, we argue that the distinction between Pavlovian and operant conditioning, as different types of learning processes, may be unnecessary. To do so we critically analyze the rationale for characterizing operant and classical conditioning as two types of learning processes, examine the similarities and differences between types of psychological events and identify which properties of substitution are particular to each type. We present the notion of function transfer as the main underlying process that accounts for all psychological interactions.