It is a grammar text about: Must / Mustn’t, Have to / Don’t have to, Need to / Don’t need to / needn’t, Should / shouldn’t, Be supposed to / had better. It teach us where and when we should...
Auxiliary verbs, as we have seen, are "helping" verbs that add structural meaning or a semantic coloring to verbs carrying the full burden of lexical meaning. All auxiliaries share the ability to be directly followed by not in negative sentences,...