Abstract
An attempt is made to provide a statement of the sufficient conditions for the functional equivalence of observable events in Psychology. Without a statement of those conditions, no explanation of functional equivalence in empirical situations can be achieved. A characterization of functional equivalence strictly in terms of the traditional S-R language is examined. This characterization is found to be inappropriate in that it entails vacuous mediators. A revision of S-R language is attempted in order to characterize functional equivalence. While this account does not entail vacuous mediators, it is unsatisfactory since it cannot be stated naturally in terms of the S-R language. It is argued that the degree to which the conditions for functional equivalence can be appropriately and naturally stated in theoretical languages provides a criterion for choosing among them as theoretical languages for psychology. A statement of the conditions for functional equivalence in terms of a TOTE analysis (see [5]) is then given. This is found to be more satisfactory than both the traditional and modified S-R analyses in that it does not entail vacuous mediators and in that a natural characterization of functional equivalence can be achieved