sentences:  Head movement, in contrast, occurs when just the head of a phrase moves, whereby this head leaves behind its dependents.Subject-auxiliary inversion is a canonical instance of head movement, e.g.On the assumption that the auxiliaries "has" and "will" are the heads of phrases – of IPs (inflection phrases), for instance – the b-sentences are the result of head movement, whereby the auxiliary verbs "has" and "will" move leftward without taking with them the rest of the phrase that they head.