This chapter discusses Wittgenstein's ideas about the relation between thought, neurophysiology and language, and about the mental capacities of non-linguistic animals. It deals with his initial espousal and later rejection of a ‘language of thought’, his arguments against the idea that thought requires a medium of images or words, his reasons for resisting the encephalocentric conception of the mind which dominates contemporary philosophy of mind and cognitive science, his mature views about the connection between thought and language, and his remarks about animals. The aim is not just to get a clear picture of Wittgenstein's position, but also to contrast it with contemporary approaches such as those of Fodor and Searle. While rejecting some of Wittgenstein's claims about the role of the brain, I defend his basic idea, namely that the capacity for entertaining a thought is conceptually tied to the capacity for displaying that thought in behaviour, rather than to the possession of language as such or to the occurrence of specific neurophysiological phenomena.

In the history of philosophy, the notion of a thought or idea has been subjected to a creeping privatisation. In the Platonist tradition, revived for example by Frege and Moore, a thought or idea is a self-subsistent abstract entity, one which inhabits a separate ontological realm beyond space and time. In Augustine and Malebranche an idea or thought turns into an archetype in the mind of God, something which for its existence depends on the divine intellect. Finally, in the wake of Descartes an idea turns into a ‘modification of the mind’, a psychic entity or occurrence which inhabits the mind of an individual, whether divine or human.

The differences between Platonism and Cartesianism can perhaps be resolved amicably by distinguishing between a thought as what is thought or believed – a so-called ‘propositional content’ – and a thought as the having of a thought, a thinking or believing. As Frege pointed out, what I think – for example, that water is potable – is true or false, independently of my thinking it. Furthermore, the very same thought can be entertained by different individuals (Frege 1892, 29–32; 1918). By contrast, the state of affairs of my thinking that p differs from the state of affairs of your thinking that p. My thinking that water is potable is a modification of me as an individual.