Third-factor explanations and Universal Grammar

This chapter discusses factors determining the structure of an I-language: genetic endowment, input/exposure to language, and principles not specific to language. The latter have become known as ‘third factors,’ which are argued to be principles that contribute to shaping the structure of grammars but that are not specific to language. Computational efficiency is one example of such a principle that has been suggested. In this chapter, the historical roots of the third factor perspective is traced and discussed. The third factor perspective in linguistics is also compared to a similar perspective in comparative biology outlined by the late Stephen Jay Gould. After a review of a few examples of what plausible third factors may be, the chapter ends with a discussion of the complex task of determining whether a given linguistic condition may be a third factor