A2
The potential form — can
How the Japanese potential form is made, why its object switches to が, and how it differs from ことができる.
Japanese has no separate word for can. The verb itself changes.
日本語が話せます。
Nihongo ga hanasemasu.
I can speak Japanese.
納豆が食べられますか。
Nattō ga taberaremasu ka.
Can you eat nattō?
How it is formed
| 飲む → 飲める | う-verb: the final u becomes eru |
| 話す → 話せる | う-verb: the same rule |
| 食べる → 食べられる | る-verb: drop る, add られる |
| する → できる | irregular |
| 来る → 来られる | irregular |
Every potential form ends in る and conjugates as a る-verb from there: 飲める → 飲めます, 飲めない, 飲めた.
The object takes が
This is the change that catches people. Ability is a state, not an action, so what you can do behaves like a subject.
日本語を話せます。
日本語が話せます。
The potential form describes a state of the speaker, and 日本語 is what that state is about. を is increasingly heard in casual speech, but が is what is taught and what is written.
ら-dropping
食べれる instead of 食べられる is extremely common in speech and still considered incorrect in writing. It is worth recognising, and worth not writing.
ことができる
The longer alternative, built on the plain form. It is more formal and slightly heavier, and it is the natural choice when the ability is a permission or a possibility rather than a skill.
ここで写真を撮ることができます。
Koko de shashin o toru koto ga dekimasu.
You can take photographs here.
Note that inside it the object keeps を — the が has moved to こと.