S主+情态动词+have+PP 对过去的行为的推测
特别提醒:情态动词表推测时
1、 can只能用于否定句和疑问句
2、 must只能用于肯定句(它的否定句和疑问句其实就用can来代替了)
3、 如句中有情态动词 + 完成时,定是对过去的推测 。
4、 句中如有表示不肯定的话语,如:I am not sure; I dont know 之类,常选may /might的各种形式
4. 记住下面几组表示反劝的特殊的表推测的形式
1). could + have + PP表示本来能做到,但事实上没有做到。 He could have finished the task on time, but the heavy snow came.
2). couldnt +have + PP表示本来不能做到,但已经做到了。 She could not have covered the whole distance, but in fact she arrived ahead of time.
3) neednt + have + pp表示本不必做的,但已经做到了。 She neednt have attended the meeting yesterday, but she did.
4.) should/ought to +have + PP表示 该做而没有做 The plant is dead. I should/ought to have given ot more water.
5) shouldnt/ oughtnt to +have + PP表示 不该做而做了。 You oughtnt to / shouldnt have taken her bike without permission.
5. 记住下面对比表:
must只能用于肯定句(它的否定句和疑问句其实就用can来代替了)
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