TO HAVE AS AN AUXILIARY VERB: Auxiliary verbs are added to make them work in others forms, such as questiosn, Negatives and others times of the sentences. * Must have to, should, ought to, need to, these are modal auxiliary verbs of obligations. There are two types of modal verbs of obligations. 1- Those that primarily express a firm obligation or necessity. Must and have to. 2-Those that express a recommendation or moral obligation. Should/ Ought to/ Need to. 1- FIRMS OBLIGATIONS: MUST/ HAVE TO. The verb MUST only exists in the simple present and present perfect forms. *While the present form can express: Obligation, necessity, certainty or strong probability. *The present perfect forms only express a strongly felt opinion or supposition. All person: Present / Present perfect Affirmative: Must Must hav...