Lingualism claims there is no thought without language. At the other end of the theoretical spectrum, strong nativist 'Language of Thought' theories hold that public language is inessential to private thought. For an adequate empirical description of the ontogeny of thought and language, however, we need an intermediate position recognizing the dialectical interplay between pre-linguistic thought, language acquisition and the development of full-fledged linguistic reason. In this article recent findings from developmental and comparative psychology are reviewed that highlight the need for such a dialectical picture. These findings concern basic cognitive capacities common to pre-linguistic infants and many non-linguistic animals, specific social-cognitive abilities in human infants that enable language acquisition, and the influence of language on the subsequent cognitive development.