Anyone devoted to poetry is likely to have experienced the vertiginous feeling of encountering a poem or a passage or a phrase which by means of originality or compression exceeds what it has hitherto seemed possible to say. Some poets are lucky enough to feel a whole imaginative circuit surge into life without deliberate intent. These are mysterious experiences - but not, surely, otherworldly ones. Craft, alertness, long thought, timing, reading, good fortune - all play their part, and Mystery is what apprentices seek to be trained in.