We may know that they came from several parts of the south of England or Scotland, for example. But we also know that accents in England and Scotland may change considerably within a five-mile (eight-kilometre) radius, and we rarely know (a) precisely how many speakers from any particular area there were or (b) precisely where the people came from. In some ways, then, we are forced to do some linguistic detective work: ‘if this is the current make-up of the local accent,’ we have to ask, ‘what can the input varieties have been?’ Answering this question demands that.
