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Mark Pagel ("Speaking Your Mind", THES, July 7) sets out some important reasons why we should prize the world's current diversity of living languages.

It is true that the process of learning a language does change a person's brain-circuitry and consequently shapes some cognitive dispositions. It is also plausible that people who learn different languages may acquire different concepts.

However, the latter cannot be established by showing that two individuals who start off the same, and who are then trained to speak different languages, generally end up with divergent discrimination-skills. For "different discrimination-skills" does not imply "different concepts". Two individuals who learn the same language pass through different personal learning-histories. Their brains are differently affected, and this may cause them to respond differently on discrimination and recognition tasks. Yet they can pick up the same concepts.

A forester sees and recognises elms better than a novice, yet both may conceptualise that elms have been decimated by Dutch elm disease.

Andrew Woodfield Department of philosophy University of Bristol