Fifty-nine 3-year-olds were tested 3 times over a period of 7 months in order to assess the contribution of theory of mind to language development and of language to theory-of-mind development (including the independent contributions of syntax and semantics). Language competence was assessed with a standardized measure of reception and production of syntax and semantics (the Test of Early Language Development). Theory of mind was assessed with false-belief tasks and appearance–reality tasks. Earlier language abilities predicted later theory-of-mind test performance (controlling for earlier theory of mind), but earlier theory of mind did not predict later language test performance (controlling for earlier language). These findings are consistent with the argument that language is fundamental to theory-of-mind development.

In this article we examine the relation between theory-of-mind development and language. It is noteworthy that the term theory of mind was first used in the psychological literature in an article attributing theory of mind to nonlinguistic creatures (Premack & Woodruff, 1978). Recently, however, there has been more skepticism regarding primates' possession of a theory of mind (Povinelli, 1999), to the point that some have expressed the view that theory of mind is impossible without language (Segal, 1998; Smith, 1996). Even if there is evidence to support the argument that some nonhuman primates have some ability to attribute mental states to conspecifics (Byrne & Whiten, 1991), there is general agreement that it is a very limited ability. In introducing Premack and Woodruff's term to the developmental literature, Bretherton, McNew, and Beeghly-Smith...