2013年职称英语考试语法指导:情态动词7 , S9 u2 M& i; G9 F# m" [+ Q& ]) nmust 和 have to % I9 T) u4 ^" l/ ?* r7 R. e must 和 have to 都可以表示“必须”,但有几点区别: 中华考试网(www.Examw。com): g' e R. s: w, a+ m/ E
(1)must 强调“内在的职责”、“义务”,而have to 强调“外界压力”、“不得已而为之”。 * K c7 M, R' u4 a
(2)have to可用于多种时态,而must一般用于现在时,其过去时与将来时分别由had to与shall / will have to代替。 i/ Q7 N7 B5 _! F2 E; ~3 o
(3)在回答must引起的问题时,如果是否定的答复,不能用mustn't,而要用needn't或don't have to,因为mustn't是“一定不要”、“一定不能”的意思。例如: - _& W: u. ?# N& J. O0 G" G4 i 1)You must come to the classroom before eight. 3 o' ]1 h: s1 q+ Y 2)It is raining hard outside, but I have to leave now. - J4 v* q1 [; {! M
3)“Must we do it now?” “No, you needn't.”