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Fodor's language of thought (LOT) hypothesis states that cognition is a process of computation over compositional mental representations. This means that thoughts are represented in a "language" (sometimes known as mentalese) which allows complex thoughts to be built up by combining simpler thoughts in various ways. It is clear from the biology of the brain that these mental representations are not present in the same way as symbols written on paper; rather, the LOT is supposed to exist at the cognitive level, the level of thoughts and concepts. For example the thought that "John is tall" is clearly composed of at least two sub-parts: the concept of John (the person), and the concept of tallness. The manner in which these two sub-parts are combined could be expressed in first-order predicate calculus:


This expression states that the predicate 'T' ("is tall") holds of the entity 'j' (John). A real proposal for what a language of thought might look like would have to be more complex than any pure logical language, since it would have to take into account complex aspects of human thought such as the propositional attitudes. These are the various attitudes people can have towards statements; for example I might believe that John is tall, but on the other hand I could merely suspect that John is tall.

The LOT hypothesis has wide-ranging significance. It implies a strongly rationalist model of cognition where many of the fundamentals of cognition are innate, and challenges eliminative materialism and connectionism.

Other philosophers have argued that our public language is used as our mental language; that a person who speaks English thinks in English. Others contend that people who do not know a public language (e.g. babies) can think, and that therefore some form of mentalese must be present by default, but is replaced by public language.


  • Ravenscroft, Ian, Philosophy of mind. Oxford University press, 2005. pp 91.

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