There is a strong empirical and conceptual relationship between language and derived stimulus relations. An empirical relationship does not indicate that derived stimulus relations depend upon language or that such relations are mediated by language. When two dependent variables are correlated, one conservative strategy is to determine whether both variables are reflective of the same basic underlying psychological process. If the two areas do overlap at the level of behavioral process, then questions about human language may also be questions about derived stimulus relations, and vice versa.
This is the basic theoretical and empirical research strategy of RFT. The overarching aim of this behavioral research has been to integrate a range of apparently diverse psychological phenomena including, for example, stimulus equivalence, naming, understanding, analogy, metaphor, and rule-following.
Relational Frame Theory adopts the view that the core defining element in all of these, and many other inherently verbal activities, is arbitrarily applicable relational responding, and moreover that such responding is amenable to a learning or operant analysis.
RFT treats relational responding as a generalized operant, and thus appeals to a history of multiple-exemplar training. Specific types of relational responding, termed relational frames, are defined in terms of the three properties of mutualand combinatorial entailment, and the transformation of functions. Relational frames are arbitrarily applicable, but are typically not necessarily arbitrarily applied in the natural language context.
Mutual entailment refers to the derived bidirectionality of some stimulus relations, and as such it is a generic term for the concept of "symmetry" in stimulus equivalence. "Mutual entailment" applies if stimulus A is related to another stimulus B in a specific context, and as a result a relation between B and A is entailed in that context. Combinatorial entailment refers to instances in which two or more relations that have acquired the property of mutual entailment mutually combine. Combinatorial entailment is the generic term for what is called "transitivity" and "equivalence" in stimulus equivalence. Combinatorial entailment applies when, in a given context, A is related to B and B is related to C, and then in that context a relation is entailed between A and C and another between C and A. For example, if A is bigger than B, and B is bigger than C, then a bigger-than relation is entailed between A and C, and a smaller-than relation is entailed between C and A. A transformation of stimulus functions applies when functions of one event in a relational network is altered based on the functions of another event in the network and the derived relation between them. Mutual and combinatorial entailment are regulated by contextual cues (C rel). The transformation of stimulus functions are regulated by additional contextual cues (C func).
The development of relational responding can be organized into a rough list that gradually becomes more and more complex. We are not presenting this list as a set of stages or steps, and we would expect them to be sequenced only in broad terms and even then only if the training history is typical. Nevertheless, this list gives a sense of the complexity that emerges from the small set of core concepts in Relational Frame Theory.
The foregoing provides a summary of the key features of RFT. The key concept that underlies Relational Frame Theory is extremely simple—try to think of relating per se as learned behavior. As the list above shows, however, applying this simple idea leads to many specific points—the nature of an arbitrarily applicable relational response, the role of context, the varieties of relational responses, the role of the nonarbitrary environment, networks of relations, the use of these abilities to solve problems, the development of self, and so on.