1.sb. can do sth./sb. could do sth/.sb. may do sth2.sb be able to do sth. /sb be capable of doing sth.不同的表达方式区别并没有很大，试着比较下：can, be able to这两者都有“能”的意思。其区别在于:1.can还可表示“可以”“可能”,即具有某种感情色彩。例如:Can I come in?我可以进来吗?That can't be true.那不可能是真的。以上两句都不可换用be able to。2.can只有现在时和过去时两种形式,而be able to则有多种时态形式。试比较下面两句:Will you be able to come tomorrow?你明天能来吗?(将来时)This factory has been able to produce newly-devised sewing machines.这家工厂已能生产新设计的缝纫机了。(完成时)3.在be able to之前可加用另外一个助动词,且多用于否定或疑问结构,而can则无此用法。4.用于否定结构, be able to表达一时情况,而can则表达往常情况。试比较下面两句:He is not able to swim today.他今天不能游泳。He can't swim at all.他根本不会游泳。5.be able to后可接系表结构,表示一种状态或性质;而can没有这种用法。例如:He was able to be cold about her now.他现在对她可能有些冷淡。6.be able to有非谓语动词形式,而can则没有。例如:I hope to be able to do the work.我希望能做这项工作。
yvette0112
