‘What is a language?’ is a much-debated question among linguists. What may count as separate ‘languages’ for specialists in one part of the world may be more similar than ‘dialects’ of a single language elsewhere. Boundaries between states can also influence how these terms are used, as can ties of nationhood or ethnicity. For many linguists, the essential test is how far people using different forms of speech can understand one another. Others, however, define language in terms of structures or as a system, within which units form a self-contained set of relations. These are governed by rules, for example. for how words are combined and ordered and for grammatical endings.