Consider the following two sentences.

A: 僕は左と右が区別できない。

B: 僕は左と右を区別することができない。

I often see B but just know A now.

How can A be possible? What kind of grammar is A?

The following sentence (from the Tanaka Corpus) inspired me to ask this question:

The boy can't tell a swallow from a sparrow.

  • A is simply wrong. People will understand what you mean, but it's grammatically incorrect.
    – sonigo
    Apr 21 '16 at 15:34
  • 4
    @sonigo What is your basis for this claim? Apr 21 '16 at 15:57
  • 2
    Consider できる as the potential form of する、 and 区別する → 区別できる makes sense.
    – oals
    Apr 21 '16 at 17:53

Both are correct. できる means exactly the same thing as することができる. You can treat it as a special potential form of する.

So it's not that できる is being attached to a noun, it's that it is taking the place of する in a する verb.

Here are a couple more examples:



Note that it's most common to mark the thing that you can do with が rather than を because, like potential forms in general, できる really means that such-and-such "is doable." You'll see を sometimes but you can consider が the the traditionally correct way to phrase it.

Hope that helps!

  • 「僕は納豆を食べられない。」と「僕は納豆が食べられない。」とどちらが正しいでしょうか。 Apr 21 '16 at 16:09
  • As I mentioned, I think most people would consider the second sentence to be the most "correct," which I put in quotation marks because in real life, modern native speakers do mark objects with 'wo' sometimes, if it is a verb that normally takes 'wo.' So my advice is, prefer the second, but be prepared to hear the first as well. Apr 21 '16 at 17:06

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