According to the French composer Albert Roussel, 'The musician is alone in the world with his more or less unintelligible language'. It is a striking image – first, because it implies that music is a language, and second, because it suggests that no one can understand it.

It's been suspected for a long time that music and language are linked in some way. Some people believe that they were, in evolutionary terms, once the same thing: that human communication began as a kind of 'musilanguage'. And music seems to be organized with something like syntax and grammar. One phrase responds to another, and some notes and chords, like words, seem to sound right if ordered in one sequence but wrong in others. Music has even been thought to reflect speech patterns of the composer's native tongue, so that for example Elgar's music has been said to reflect the patterns of spoken English. There is now good evidence to support this: both in rhythm and in the way pitch changes, there are differences between English and French music that mirror those in the spoken language.

One of the main reasons why music is compared with language, however, is that both seem to have a hierarchical, nested structure. There are musical equivalents of clauses and subclauses, sentences, paragraphs and chapters, all of which help to organize the sound and in some sense lend it meaning. What's more, our brains seem to use much the same apparatus to understand linguistic and musical syntax: in both cases, if what we hear violates our normal syntactic expectations, the brain's language-processing centre sends out a warning signal of something wrong, the neural equivalent of saying 'Huh?'