2013年职称英语考试语法指导:情态动词7 W+ d5 J: P3 p# U7 W1 v9 Z2 u$ [must 和 have to $ m0 N' h- b3 V/ O w0 y
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)% F. ?6 Z. a* p5 O7 v# j! m
(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”。 " g; f, ]/ S" A; l3 ^
(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。 7 G- Y" I; o" z( b4 D! r( ]7 V (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: : [4 W0 o) z. v4 N- k 1)You must come to the classroom before eight. 9 {# E" i! G6 N/ \; @$ _$ V 2)It is raining hard outside, but I have to leave now. + ?$ ^: x: @0 x5 u5 j* n 3)“Must we do it now?” “No, you needn't.”