Practical English Usage (1980)

Fourth edition Michael Swan's reference is the book teachers reach for when a student asks something the coursebook does not cover. Its 600-plus entries are built around the questions learners actually ask, and the fourth edition splits them into a grammar half and a vocabulary half, so you can look up a structure or a confusing pair of words with equal ease. It is written for teachers, trainee teachers and advanced students rather than beginners, and it is a book you look things up in rather than work through; Swan's grammar tests come as a separate companion. It covers British and American differences, which makes it a useful answer to "is this wrong, or just American?"