can can't must mustn't may might should

①表示“必需”“一定”“必要性” 1.must表主观上的必需,而have to表职责或义务,强调客观. 2.need作为情态动词用于疑问句或否定句.Need you……?的答句是Yes,I must.或No,I needn't(don't have to)对问句表示有必要做某事的肯定答语是Yes,you must/have to.否定答语是No,you needn't./don't have to/don't need to. ②表示“推测或