Mentalese the language of thought (the title of a book by Fodor, 1975) or of ‘brain writing’ (a term of Dennett’s); specifically, a languagelike medium of representation in which the contents of mental events are supposedly expressed or recorded. (The term was probably coined by Wilfrid Sellars, with whose views it was first associated.) If what one believes are propositions, then it is tempting to propose that believing something is having the Mentalese expression of that proposition somehow written in the relevant place in one’s mind or brain. Thinking a thought, at least on those occasions when we think ‘wordlessly’ (without formulating our thoughts in sentences or phrases composed of words of a public language), thus appears to be a matter of creating a short-lived Mentalese expression in a special arena or work space in the mind. In a further application of the concept, the process of coming to understand a sentence of natural language can be viewed as one of translating the sentence into Mentalese. It has often been argued that this view of understanding only postpones the difficult questions of meaning, for it leaves unanswered the question of how Mentalese expressions come to have the meanings they do. There have been frequent attempts to develop versions of the hypothesis that mental activity is conducted in Mentalese, and just as frequent criticisms of these attempts. Some critics deny there is anything properly called representation in the mind or brain at all; others claim that the system of representation used by the brain is not enough like a natural language to be called a language. Even among defenders of Mentalese, it has seldom been claimed that all brains ‘speak’ the same Mentalese. See also PHILOSOPHY OF LANGUAGE ; PHILOSOPHY OF MIND ; SELLARS , WILFRI. D.C.D.