Language, according to Jackendoff, is more than just an instrument of communication and cultural transmission. It is also a tool which helps us to think. It does so, he suggests, by expanding the range of our conscious contents and hence allowing processes of attention and reflection to focus on items (such as abstract concepts and steps in chains of reasoning) which would not otherwise be available for scrutiny. I applaud Jackendoff s basic vision, but raise some doubts concerning the argument. In particular, I wonder what it is about public language that uniquely fits it to play the functional role which Jackendoff isolates ” why couldn't expression in a private inner code induce the same computational benefits? I suggest a weaker position in which the communicative role of public language moulds it into a suitably expressive resource, such that natural language emerges as the logically and technologically contingent filler of a functional role which could, in principle, be filled by other means. I also compare and contrast Jackendoff's position with some related ideas due to Daniel Dennett and others, concluding with a sketch of my own view of language as an external artifact whose computational properties complement those of the basic biological brain.