The word that translate to " can" in a sentence?


I am not sure what is the right the expression to use when I want to include
"can" in a Japanese sentence:

for example :

  1. > Can I buy a fruit? 

is

> Kudamono o kau koto wa dekimasu ka?

_however_

  2. > Can I ask you a question? 

is

> Shitsumon shite mo īdesu ka?

Isn't the expression "dekimasu ka" mean "can I" with the "I" part understood?
Why is it not on the second sentence? Is there any grammar rule or is
something to be memorized?




There are a few nuance things to consider. The most important one is that
there isn't a 1:1 correlation of all words between Japanese and English.
Therefore, a specific word like "can" isn't always exactly translated as one
specific word into Japanese. There are, however, ways to express this kind of
expression with different words. Think on how in English, there are also ways
to reword these questions:

> Can I buy a fruit? -> Am I able to buy a fruit?  
>  Can I ask you a question? -> Is it alright if I asked you something?

The best approach is to find out how to ask these questions in Japanese, and
learn the nuances between the different applications in relativity to other
similar questions within Japanese.

As in your example:

> 果物｛くだもの｝を **買｛か｝うことができます** か。  
>  (verb) + ことができる = to be able to do (verb)

Note that this particular structure emphasizes on your personal ability to be
able to do something rather than the morality or accessibility of doing
something. It also has no bearing on whether this affects another party, this
is strictly on **your own ability** at a specific place and point in time.
This is the kind of "can" question that is closest to a true "can" form, where
できる = to be able to do = can.

Keep in mind that the scope of the ability is referring to the subject of the
sentence, which in this case is implied to be you. If you ask this to someone,
you're asking about **their ability** instead.

As for your other example:

> 質問{しつもん}し **てもいいですか** 。  
>  (て-form verb)+もいいですか。 = Is it alright if I (do verb)

This is the kind of "can" question where you are **asking for permission** to
perform an action. The emphasis here is on the response of the other party
onto which you are asking this.

You might liken these differences to when teachers (may have) used to hark on
you about saying "May I" instead of "Can I" because the response to "Can I go
to the bathroom?" may have included a very snarky and sarcastic "You CAN go to
the bathroom, but _you may not go_." (meaning, you have the ability to go but
_you are not allowed_ ).

