Japanese Verb Conjugation - Potential

The general pattern is u becomes eru.

Usage

The potential is used to express that one has the ability to do something. Direct objects are marked with the particle が ga instead of を o. For example 日本語が読める nihongo ga yomeru: "I can read Japanese".

It is also used to request some action from someone, in the exact sense of the English "Can you ... ?" For example 「コーヒー買える？」 koohii kaeru?: "Can (you) buy (some) coffee?" However, sometimes in English "Will you...?" and "Can you ... ?" is used interchangeably to make requests. Though it is possible in Japanese, 「コーヒー買う？」 koohii kau?, it is very casual and might also mean simply "Are you buying/Will you buy coffee?" in very dry factual sense.

Unlike in English, the potential is not often used to express permission (as in the sentence "Can I eat this apple?") as it is almost always understood to mean "Do I have the ability to eat this apple?": 「このりんごが食べられる？」 kono ringo ga taberareru?. And since the -reru form is more often used in speech than the more correct passive potential form -rareru, and subjects are often implied in Japanese, it may implicitly be asking (in this case) if the apple is edible. So, to seek permission, a more polite form is used, such as the -てもいい -te mo ii or more casual -ていい "-te ii"" usage of the -て -te form, resulting in something literally more like "Is eating this apple OK?" 「このりんごを食べてもいいですか？」 Kono ringo o tabete mo ii desu ka? or 「このりんごを食べていい？」 Kono ringo o tabete ii?.

The potential -ru ending conjugates as a vowel stem verb.

There is no potential equivalent for です; other constructions for expressing may-be situations are used:

• Using かもしれない expression. For verbs: 「明日降るかもしれない」 ashita furu kamo shirenai "It may rain tomorrow.", i-adj: 「旅行は高いかもしれない」 ryokou wa takai kamo shirenai "The journey is perhaps expensive.", na-adj: 「大切かもしれない」 taisetsu kamo shirenai "(This thing is) probably important."
• Using adverbs. 「恐らく降る」 osoraku furu "It probably will rain", 「たぶん降る」 tabun furu "Perhaps it will rain"