‘Language in space and time’ explores the topic of linguistic change. It is a fact, attested everywhere, that language changes, with vocabulary, grammar and pronunciation all being affected. That is why two languages which were once one can, in time, become so different. It must also be the reason why there are ‘languages’ at all. Within limits that might be genetically determined, language (singular) diversified by gradual changes, over a few tens of thousands of years, into the precursors of the languages (plural) which we can observe now. We have to assume that, from the outset, it carried the seeds of variability. Why, however, did change have to follow?