I present the symbol grounding problem in the larger context of a materialist theory of content and then present two problems for causal, teleo-functional accounts of content. This leads to a distinction between two kinds of mental representations: presentations and symbols; only the latter are cognitive. Based on Milner and Goodale’s dual route model of vision, I posit the existence of precise interfaces between cognitive systems that are activated during object recognition. Interfaces are constructed as a child learns, and is taught, how to interact with its environment; hence, interface structure has a social determinant essential for symbol grounding. Symbols are encoded in the brain to exploit these interfaces, by having projections to the interfaces that are activated by what they symbolise. I conclude by situating my proposal in the context of Harnad’s (1990) solution to the symbol grounding problem and responding to three standard objections.