This book is about exploring the English verb, not explaining it. The difference is important. "Explaining" assumes one person knows, and the other does not. It suggests a one-way process, which starts from a place decided by the person who knows. "Exploring" suggests the possibility of going wrong, the need to re-trace our steps, a process of guessing, checking and discovering together. Some of our guesses are right, and others wrong. The emphasis is on a dynamic and co-operative process.
So often "explaining grammar" is a waste of time, which confuses rather than helps. I hope teachers will be influenced by this book to change the emphasis of work that they do with their students from explaining to exploring.