一、明显区分: l.只可用can(could),表示“能力” (体力、知识、技能) 例:①i can swim now,but i couldn’t last year. ②can you play me piano?yes,i can. may:用于祈使句,表示祝愿。 may you succeed! must:表示必须 you must come in time. 2.can(could)适用于各种句型和人称。 例:①肯定句:i(you,he)can swim. ②否定句:i(you,he)can’t swim. ③疑问句:can i(you,he)swim? 二、表示“请求”或“许可”。 can、may、must都可用,但语气和程度不同。 1.can(could)用于各种句型和大部分人称。 例:①肯定句:you(he,we)can go now. ②否定句:you(he,we)can’t go now. ③疑问句:can i(you,he)go now? yes,you can.(no,you can’t.) 2.may(might)用于各种句型,但在肯定句和否定句中不用于第一称;在疑问句中不用于第二人称。 例:①肯定句:you(he)may go now. ②否定句:you(he)may not go now. ③疑问句:may i(he)go now? 正规回答:(表定)yes,you may.(yes, you can) (否定)no,you may not.(no,you can’t./no,you mustnt.) 口语化回答:(肯定)yes,please.(certainly.) (否定)no,please don’t.(no,of course not.) 3.must用于各种句型和大部分人称。 例:①肯定句:i(you,he)must go now. ②否定句:you(he)mustn’t go now. ③疑问句:must(you,he)go now? 肯定回答:yes,you must. 否定回答:no,you needn’t.(no,you don’t have to.) 4.试比较: you may not smoke here.(不可以)语气轻 you can’t smoke here.(不能)重 you mustn’t smoke here.(决不可)最重 三、表示“可能”、“或许”和“推测”之意。can、may、must都可用,但语气和程度不同。 l.can (could)常用于否定句和疑问句中,could表示的“可能性”更小。 例:①否定句:it couldn’t be him,for he’s at the library. ②疑问句:can he have gone out? what can they be doing now? 2.may(might)用于肯定句和否定句中,might表示的“可能性”更小。 例:①肯定句:he may be right. ②否定句:she may not have e yet. 3.must用于肯定句中。 例:①you must be very hungry.(对现在情况猜测) ②everything is clean and tidy.someone must have cleaned my room.(对过去事实的猜测) 4.试比较: he might not have gone out.(或许没有) he can’t have gone out.(不可能) he must have been in the room.(一定、准是)
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