できる vs ~えます form for "can", "able to"


A couple of days ago I tried to express "I can ..." where "..." was some some
verb or verb phrase.

I used the ～て form of the ... verb followed by 出来ます but was told instead to
change the form of the ... verb from ～います to ～えます.

So now it seems to me that both 出来る and ～えます can have similar functions. What
is the real difference and how can I know which to use when?




Short answer:

  1. 得{え}る or うる is more literary. ことができる is slightly more formal than られる and both fit for everyday use.

  2. ことができる and られる can only be used to describe humans' ability so they don't fit well with non-volitional verbs (無意志動詞). える or うる can also be used to describe possibility. E.g. ×あられる ○あり得る 

  3. Both ことができる and られる can be used when you are not allowed to do something, you don't have enough knowledge or skills to do something, or you don't want to do something. But it seems that people tend to use ことができる when they are not physically unable.

  4. There are very rare cases that ことができる can occasionally be used with non-volitional. られる cannot.

* * *

I just realized your えます might refer to the -(r)eる potential form rather than
得ます{えます}.

  1. られる and -(r)eる are basically the same. But られる has more meanings than -eる, e.g. it can be used as a passive form.

  2. -(r)eる works for almost all types of verbs, while られる generally only works with 一段動詞.

  3. Although the meaning are the same, られる is longer than -(r)eる, which sometimes make it less favorable in certain situations. e.g.
[code]      The number of results given by Google:

     230 開けようとしても開かない
     74  開けられない
     13  開けようとしても開けることができない
    
     67  声を出そうとしても出ない
     20  声を出そうとしても出せない
     3   声を出そうとしても出すことができない
    
     277 声が出ない
     255 声が出せない
     162 声を出すことができない
    
[/code]

