What I am concerned with in this chapter is not language in the most general sense of the term ‘language’ but with what can be described more fully as natural human language. Arguably, this fuller description is redundant in respect of either or both of the two adjectives, ‘natural’ and ‘human’. Indeed, this is the view that most linguists and many philosophers of language would take. But it is worth making the point explicit and concentrating for a moment upon the implications of both of the qualifying adjectives, without prejudice to the question of whether there is any language, properly so called, that is non-natural or non-human.

Without dwelling upon the details let us say that a natural language is one that has not been specially constructed, whether for general or specific purposes, and is acquired by its users without special instruction as a normal part of the process of maturation and socialization. In terms of this rough-and-ready operational definition, there are some thousands of distinct natural human languages used in the world today, including English, Quechua, Dyirbal, Yoruba and Malayalam – to list just a few, each of which is representative, in various ways, of hundreds or thousands of others. But Esperanto, on the one hand, and first-order predicate calculus or computer languages such as algol, fortran and basic, on the other, are non-natural. Many non-natural languages are parasitic, to a greater or less extent, upon pre-existing natural languages.