第一个区别 时态在一般语句里面couldn't表过去时can't表现在时,can 是现在是.could 是过去式
第二个区别 could 比can 多一个意思就是情态动词 ,大概意思就是 couldnot 有个 委婉,这类的意思 cannot 没有,在请求语句里面couldn't比can't较委婉
can't/couldn't表示推测时,意思是“不可能...”,语气非常坚决的否定推测.
根据动作发生的时间,一般分为以下三种情况:
1)进行式(对正在发生的事情的否定推测):can't be doing sth
如:It's already ten o'clock.My father can't be sleeping now.
2)完成式(对过去的动作的否定推测):can't/couldn't have done sth
如:He is at schoool,so he can't/couldn't have stayed up last night.
3)一般式(对现在/将来情况的否定推测):can't do sth
如:Your answer can't be true.
can/could表示推测时一般只用于否定句/疑问句,但是也可用于肯定句,只是比较少见.
其中could不表示过去式,而表示可能性较小.
如:I think the work can be completed ahead of time.我认为这项工作能提前完成.
在请求语句里面couldn't比can't较委婉在一般语句里面couldn't表过去时can't表现在时
1,can could 都是情态动词,其后都加动词原形,can't couldn't 也一样,都加动词原形
2,同时could 是can 的过去式,二者又可表示具备"能力", can指现在具备的能力,could指过去具备的能力
can't/couldn't表示推测时,意思是“不可能...”,语气非常坚决的否定推测。
根据动作发生的时间,一般分为以下三种情况:
1)进行式(对正在发生的事情的否定推测):can't be doing sth
如:It's already ten o'clock. My father can't be sleeping now.
2)完成式(对过去的动作的否定推测):can't/couldn't have done sth
如:He is at schoool, so he can't/couldn't have stayed up last night.
3)一般式(对现在/将来情况的否定推测):can't do sth
如:Your answer can't be true.
can/could表示推测时一般只用于否定句/疑问句,但是也可用于肯定句,只是比较少见。
其中could不表示过去式,而表示可能性较小。
拓展资料
can't
1、I'm afraid I can't remember the way
我恐怕不记得路了。
2、I don't want to leave, but I can't go on.
我不想离开,但我继续不下去了。
3、I can't drink any more.
我不能再喝了。
4、Don't tell me you can't remember.
不要告诉我你记不起来了。
5、I can't eat any more; I'm full up.
我不能再吃了,我已经很饱了。
couldn't
1、Jamie e-mailed me to say he couldn't come
杰米给我发了电子邮件,说他不能来了。
2、I couldn't tell if he had been in a fight or had just fallen down
我不知道他是和人家打架了,还是仅仅摔了一跤。
3、I couldn't imagine why he would want to be alone with me
我想象不出为什么他会想和我独处。
4、They put a screen in front of me so I couldn't see what was going on.
他们在我面前竖了一面屏风,所以我看不到发生了什么事情。
5、I couldn't get back to sleep.
我再也睡不着了。
在请求语句里面couldn't比can't较委婉
在一般语句里面couldn't表过去时can't表现在时
can't
1、I'm afraid I can't remember the way
我恐怕不记得路了。
2、I don't want to leave, but I can't go on.
我不想离开,但我继续不下去了。
3、I can't drink any more.
我不能再喝了。
4、Don't tell me you can't remember.
不要告诉我你记不起来了。
5、I can't eat any more; I'm full up.
我不能再吃了,我已经很饱了。
couldn't
1、Jamie e-mailed me to say he couldn't come
杰米给我发了电子邮件,说他不能来了。
2、I couldn't tell if he had been in a fight or had just fallen down
我不知道他是和人家打架了,还是仅仅摔了一跤。
3、I couldn't imagine why he would want to be alone with me
我想象不出为什么他会想和我独处。
4、They put a screen in front of me so I couldn't see what was going on.
他们在我面前竖了一面屏风,所以我看不到发生了什么事情。
5、I couldn't get back to sleep.
我再也睡不着了。
看用在什么地方了,语气方面,couldn't语气较委婉,can't语气较强硬。另外couldn't还可以是can't的虚拟语气