Most language course-books these days are frightened of grammar, with the result that many learners are starved of "what goes on under the bonnet". This excellent book lays everything out logically, so that one can see the relationships form, and words aren't just words, but have their place in the grammatical firmament. Absolutely invaluable if one intends to use a different part of a verb, or a different possessive form, from that served up by Teacher. The book isn't quite pocket-sized (unless you're a kangaroo), but it's small enough to be good fodder for those dull commuter journeys by train, bus or Tube.