I’m just wondering in what situations these verbs would vary. At first I thought that they would be used for differentiating present/nonpresent tense, but both verbs can be conjugated in any of those ways. Is できる used more in instances of describing another person/your own actions? For example, in the sentence “気づくことができなかったんだ” could you not replace “できなかった” with “しなかった”? I know the difference is to do vs can do, but I’m having a hard time figuring out specifically how these verbs differ in contexts such as these. Is しなかった “did not do” and できなかった “cannot do”? Is there any real difference/would it be wrong to use either? In JLab, the description for dekinakatta is “past negative of dekiru (to be able to do).” Is this not the same as the past negative of suru?
3 comments
できる and する are very different verbs. できる means to be able to do, whereas する is just to do.
する is doing more so
できる is will do
The previous comment is not 100% correct, unfortunately. The verb you’re having trouble with is する; it’s something akin to an irregular verb and has many uses and meanings depending on which particles it’s paired with, etc.
But its basic meaning is “to do.” So, できる is the (irregular) potential form of する and *not a different verb.* From the plain potential form, you can conjugate past, negative and so on.
しなかった is the plain past negative form of する meaning “did not do.”
できなかった is the plain past negative potential form of する meaning “could not do.”
Scroll down to the [conjugation table](https://www.tanoshiijapanese.com/dictionary/conjugation_details.cfm?entry_id=14743) for する; you’ll encounter more of its usage, meanings and conjugations as you move on with your Japanese studies.