can,or could?问:Michael Swan 在 Practical Eng-lish Usage 一书中说,can 与动词不定式完成时(perfect infinitive 连用时,只能用于疑问句和否定句,在肯定句中须用 could。但在 Quirk 等人编写的 A UniversityGrammar of English Workbook 里面,编者似乎认为 There can have been an acci-dent.也可以成立。这两种说法是否矛盾?答:一般的用法手册或教科书上说的都和 Swan 所说的一致。Qurik 他们也只是在练习里表示 can+have done 是可能的。can 讲可能性的时候,比 may/might/could都带有更多的肯定成分,这一点大概是语法家们所公认的。假定有人说:There can’t Q: In his book Practical Eng-lish Usage, Michael Swan said that when used with perfect infinitive, can and can only be used in interrogative and negative sentences, and could not be used in affirmative sentences. However, in the A University Grammar of English Workbook by Quirk et al., The editors seem to think there is a contradiction between these two statements. A: The general usage manuals or textbooks say both Swan said the same .Qurik they are only in practice that can + have done is possible .can say more likely than may / might / could have more positive ingredients, which is probably a grammar It is generally accepted that there are people who say: There can not