I was recently involved in the assessment and translation into French of a medical questionnaire for an international organisation specialising in epidemiology. A whole morning had been earmarked for the task, more than long enough, the organisers believed, to deal with forty short items. We started on Item 1 dead on nine with brisk enthusiasm and by our one o'clock lunchtime ... we were still on Item 1. This asked respondents to agree or disagree with the following statement:

I like who I am.

There we were, a committee made up of specialists in an extremely wide and imposing range of disciplines – medicine and translation, statistics and ethnolinguistics, sociology and psychology – completely floored by an utterance that contains only five words, all of them monosyllabic and amongst the commonest words in the language. And the really awful bit, the bit that had us avoiding eye contact with one another, drinking too much coffee and hoping it was fire-drill day, was that not only could we not translate it, we could not even understand why we could not translate it. Even worse, whilst we all thought we understood it, no one could say what it meant.

Reactions to this state of affairs varied. One colleague exclaimed, 'That expression is so American!', which obviously explained matters to his own satisfaction. Another invoked the name of Descartes. A third wondered if thirty-nine questions wasn't enough, really? We had run head-on into an epistemological labyrinth and could not find our way out, our shouts only echoing endlessly off the walls. Even those who were able to accept the idea of cultural variation in concepts of personhood at some highly generalised theoretical level had great difficulty in believing that this could result in such particularised differences in self-expression, that such a simple phrase could be so difficult.

It is these issues, the relationships between language and identity, between languages and the architecture of the psyche, between the individual and the ineffable, that are addressed in this remarkable book.