[...] the theory of change put forward in Andersen 1973 [Andersen, Henning, 1973, “Abductive and deductive change”, “Language” 49, pp. 567-595]. This theory distinguishes two modes of innovation, abductive and deductive. Abductive innovations are innovations that arise in the process of (abductively) inferring elements of a grammar from speech. Abductive innovations result in correspondences between elements of a grammar (G-2) and homologous elements of the grammar (G-1) from whose output G-2 was inferred. Deductive innovations are innovations that arise in the (deductive) process of deriving a phonetic output from a semantic representation (which in turn can be viewed as the output of a pragmatic competence) by means of a grammar. Deductive innovations are observable as correspondences between the output (O-2) of one grammar (G-2) and the output from which G-2 was inferred.
- Andersen (2004), Pag. 403