Monday, December 9, 2019

Potential Verbs

In Japanese, a kanou doushi 可能動詞, "potential verb," is a shimo-ichidan verb conjugated from a godan verb consonant stem plus ~eru ~eる, which adds an "able to" meaning to it.

For example: yomeru 読める, "to be able to read," or "can read," is the potential verb variant of yomu 読む, "to read."

It is, in practice, the potential form of godan verbs.


The kanou doushi are highly regular: they're always formed from the consonant stem of a godan verb, plus an ~eru suffix. With ~u ending verbs there's no consonant, so it just replaces the ~u. Observe:
  • kau, kaeru
    買う, 買える
    To buy. To be able to buy.
  • kaku, kakeru
    書く, 書ける
    To write. To be able to write.
  • oyogu, oyogeru
    泳ぐ, 泳げる
    To swim. To be able to swim.
  • katsu, kateru
    勝つ, 勝てる
    To win. To be able to win.
  • shinu, shineru
    死ぬ, 死ねる
    To die. To be able to die.
  • asobu, asoberu
    遊ぶ, 遊べる
    To play. To be able to play.
  • yomu, yomeru
    読む, 読める
    To drink. To be able to drink.
  • korosu, koroseru
    殺す, 殺せる
    To kill. To be able to kill.
  • toru, torenai
    取る, 取れない
    To take. To be able to take.

Note that, TECHNICALLY, the potential verbs aren't verb forms. That's why they're called "potential verbs," and not "the potential form of verbs." In practice, none of this matters, so I'll explain the stuff that matters first, and we deal with the technicalities later.

The potential verbs are conjugated just like any ichidan verb. This means you can create the negative form, and so on, by using jodoushi and whatnot, just like any other ichidan verb. Observe:
  • yomeru
    To be able to read.
    • Potential verb.
  • yometa
    Was able to read.
    • Past form of the potential verb.
  • yomenai
    To not be able to read.
    • Negative form of the potential verb.
  • yomenakatta
    Was not able to read.
    • Past negative form of the potential verb.
  • yometai
    To want to be able to read.
    • Desiderative form of the potential verb.
  • yometemo
    Even if [you] were able to read.
    • ~te-mo form of the potential verb.

Note that it's easy to mistake the negative form of the godan verb with the negative form of the potential verb, which is a shimo-ichidan verb. For example:
  • yomu
    To read.
  • yomeru
    To be able to read.
  • yomanai
    To not read.
    • The mizenkei of yom-u, yom-a~, plus ~nai.
  • yomenai
    To not be able to read.
    • The mizenkei of yome-ru, yome~, plus ~nai.

Above, the only difference between the two verbs and meanings is whether you have a ma ま or me め, so it's important to pay attention to the vowel before the ~nai. If the vowel is ~a, yom-A-nai, then it's the godan verb. If the vowel is ~e, yomE-nai, then it's the potential verb.

The so-called kanou doushi 可能動詞, literally "potential verbs," aren't the only thing that work like, well, potential verbs.

For example, kikoeru 聞こえる means that something "is heard," but if it "is heard," that means it "can be heard," so it works kind of like the potential of kiku 聞く, "to hear," and people will prefer to construct sentences with kikoeru, rather than with kikeru 聞ける, "can hear."

Some verbs that look like potential verbs aren't potential verbs.

For example, tsudzuku 続く, "to continue," and tsudzukeru 続ける, "to continue [doing something]," form an intransitive-transitive, ergative verb pair. So if you see tsudzukeru 続ける, it probably won't mean "[something] can continue," it will just mean "[someone] continues [something].


The grammar of potential verbs is a bit complicated, and it partially depends on whether the verb has a subject and object, it's transitive, or it only has a subject, it's intransitive.

Let's start with a simple case: an intransitive verb, like warau 笑う, "to laugh." It only has one subject, the person who is doing the laughing, the person who laughs. Observe and compare how the potential verb, waraeru 笑える, is used:
  • Tarou wa warau
    Tarou laughs.
  • Tarou wa waraeru
    Tarou can laugh.
    Tarou is able to laugh.
  • Tarou wa waraenai
    Tarou can't laugh.
    Tarou isn't able to laugh.

As you can see above, there's nothing really special about potential verbs so far. It works just like any other verb form, even though it isn't a verb form. You change the ending of the verb, it changes the meaning of the sentence, you don't really need to change anything else.

In English, translating it to either "can" or "is able" works. It isn't like there's much difference anyways.

Like any other verb, it can also be used in relative clauses in order to qualify a noun:
  • {waraenai} hito
    A person [who] {can't laugh}.
    People [who] {can't laugh}.

Most of the time the potential isn't necessary in relative clauses, because if you say someone "doesn't do" something, it's just kind of implied they can't do it.
  • {warawanai} hito
    A person [who] {doesn't laugh}.
    People [who] {don't laugh}.

Also, most of the time you encounter a potential verb it will be in the negative, because people seldom talk about what they can do, and often point out what they can't do. Which is kind of depressing, to be honest.

Can Become

The most useful to verb to learn the potential of is "to become," naru なる, which would be "can become," nareru なれる.

The verb naru なる is intransitive and takes an adverb instead of direct object. The adverb is either the adverbial form of i-adjectives, which ends in ~ku ~く, or the adverbial copula ni, which replaces the predicative copula da, after a na-adjective or noun.
  • tsuyoi
    To be strong.
    [He] is strong.
  • tsuyoku naru
    To become strong.
    [He] will become strong.
  • tsuyoku nareru
    To be able to become strong.
    [He] can become strong.
  • tsuyoku narenai
    To not be able to become strong.
    [He] can't become strong.
  • shiawase da
    To be happy.
    [He] is happy.
  • shiawase ni naru
    To become happy.
    [He] will become happy.
  • shiawase ni nareru
    To be able to become happy.
    [He] can become happy.
  • shiawase ni narenai
    To not be able to become happy.
    [He] can't become happy.

To Become Able

To say "to become able to do something" in Japanese, the phrase ~you ni naru ~ようになる is necessary.

As we already know, naru なる comes after an adverb, and you can make adverbs out of adjectives and nouns. But potential verbs are verbs, they are neither adjectives nor nouns, so you can't make adverbs out of them.

In order to use the potential verb with naru なる, an intermediary step is necessary, where the verb is turned into a noun, so it can be turned into an adverb by the ni に adverbial copula.

In this step, the potential verb goes inside a relative clause that qualifies the formal noun you よう, and then this you よう is turned into an adverb. Observe:
  • Tarou wa {waraenai} hito da
    Tarou is a person [who] {can't laugh}.
  • Tarou wa {waraeru} hito ni naru
    Tarou will become a person [who] {can laugh}.
  • Tarou wa {waraeru} you ni naru
    Tarou will become in a way [that] {is able to laugh}.

Above, you よう replaces the noun hito 人, and the meaning of the phrase is still basically the same, but in Japanese the you よう is preferred in this sort of case.

Don't bother translating you よう to English. It's a noun in Japanese syntax, but it doesn't really translate to a noun in English.

The verb naru なる, of course, can be conjugated.
  • Tarou wa {waraeru} you ni natta
    Tarou became {able to laugh}.
  • Tarou wa {waraeru} you ni naritai
    Tarou wants to become {able to laugh}.

You can even use the potential verb nareru なれる instead, and then you have two potentials in one sentence.
  • Tarou wa {waraeru} you ni narenai
    Tarou can't become {able to laugh}.


In potential sentences that should have a transitive verb, sometimes the verb becomes intransitive, and the sentence becomes a double subject construction, and then the particles used in the sentence change. Observe:
  • Tarou wa manga wo yomu
    Tarou reads manga.
  • Tarou wa manga wo yomeru
    Tarou can read manga.
  • Tarou wa {manga ga yomeru}
    {Manga is read-able} is true about Tarou.
    Tarou can read manga.
  • Tarou niwa {manga ga yomeru}
    {Manga is read-able} is true for Tarou.
    Tarou can read manga.

As you can see above, there are a few different ways of saying basically the same thing in Japanese.

The first way is marking the subject with the ga が particle, except when it's the topic of the sentence, it's marked by the wa は particle instead, and the direct object with the wo を particle.

That's just how the original verb, yomu, works. Nothing special about it.

The second way is when you have two subjects. Then the large subject, Tarou wa, is who can or can't do something, while the small subject, manga ga, is the thing to what something can or can't be done.

You can't use this pattern with yomu, only with yomeru.
  • *Tarou wa manga ga yomu

This happens because yomeru has a meaning close to an adjective in the double subject construction, despite being a verb. The sentence says, literally, that "manga is read-able." The predicate "read-able" predicates the small subject "manga."

And then the predicative clause "manga is read-able" predicates the large subject "Tarou." That means manga isn't universally read-able—it's read-able to Tarou, but maybe it's not read-able to Hanako. In other words, Tarou can read manga, but maybe Hanako can't.

Basically, yomeru translates to "can read" if there's one object (wo を), but translates to "is read-able" if there are two subjects (wa は plus ga が, or ga が plus ga が), but this "is read-able" sounds weird in English, so in the end it translates to "can read," after all.

Needless to say, Japanese grammar is weird and doesn't work like English, so this sort of thing happens.

Now, about the difference between these two particles, ga が vs. wo を, there basically are none, as far as potential verbs are concerned. Even so, you may want to use ga が, despite it being harder to understand from an English perspective.

Many resources will teach you to use only ga が with potentials, but in practice, a lot of natives use wo を with potentials for some reason. Both seem acceptable.
  • piano wo hiku
    To play the piano.
  • piano wo hikeru
    To be able to play the piano.
  • piano ga hikeru
    (same meaning.)

It seems that younger natives are more prone to use wo を particle instead of the ga が particle in sentences like the one above, showing a shift in how the particles are used in Japanese.(東山, 2007:77)

Do note that, the potential of suru する, dekiru できる, is pretty much only used intransitively, with ga が, and never with wo を, so it makes sense to just use ga が every time with potentials in order to avoid confusion.
  • benkyou wo suru
    To do the study.
    To study.
  • *benkyou wo dekiru
  • benkyou ga dekiru
    To be able to do the study.
    To be able to study.

In regards to niwa には, which is the topicalized version of the ni に particle, marking the dative subject, the meaning is still pretty much the same.

The difference is that niwa には emphasizes that something is do-able for someone, and not for someone else. For example:
  • Tarou niwa manga ga yomeru
    Manga is read-able for Tarou.
    Tarou can read manga.
  • Hanako niwa yomenai
    [It] isn't read-able for Hanako.
    Hanako can't read [it].

Basically, when you're describing what someone can or can't do, wa-ga is used. Someone can play the piano. Someone can speak Japanese. And so on. Wow, so many abilities. But when you already have something that is done, and you're talking about who can or can't do it, you use niwa-ga.

For example: someone does something, and someone else says "I can't do something like that." And niwa will be used. Because they aren't talking about themselves, they're talking about the feat. They're saying: "that thing, it isn't possible for me."

Besides these particles, there are all sorts of other particles that can be used with verbs, and that don't really work particularly different with potential verbs.

For example, the ni に particle also marks the indirect object, the destination, etc., in which case it works just the same, it doesn't matter if the verb is potential or not. For reference:
  • {gakkou ni ikeru} you ni natta
    Became {able to go to school}.
    • gakkou ni iku
      To go to school.
  • kanojo ni aeru
    To be able to meet her.
    • kanojo ni au
      To meet her.
  • yuurei to hanaseru
    To be able to talk with ghosts.
    • yuurei to hanasu
      To talk with ghosts.
  • maou niwa katenai
    Against the demon lord, [he] can't win.
    • maou ni katsu
      To win against the demon lord.
  • koko dewa ienai
    In here, [I] can't say [it].
    • koko de iu
      To say [it] here.
  • tooku e wa arukenai
    To not be able to walk toward [somewhere] distant.
    • tooku e aruku
      To walk toward [somewhere] distance.

vs. Potential Form

Now that the important part is taken care of, let's talk about the unimportant part: why are potential verbs not the potential form of verbs?

In godan verbs, the stem is said to end at the consonant. For example, the stem of yomu ends at the m consonant. We know this because every form we derive from yomu starts with yom, so yom~ is the stem, it's the common denominator.
  • yomanai
    To not read.
  • yomitai
    To want to read.
  • yomu
    To read.
  • yomeba
    If reads.
  • yomou
    Let's read.

Problem is, Japanese doesn't have a native way to spell out the consonants. There's romaji, but romaji isn't native Japanese, so it doesn't count. Since they can't say the stem of the verb ends in the consonant m, what do they say instead?

They say that the verb has multiple stem-like forms, each ending with a different vowel. You have five vowels, so five stems: ma-mi-mu-me-mo まみむめも. That's why it's called a godan 五段 verb, a "five column" verb. Because if you laid it as a table, a-i-u-e-o are the columns. (see: gojūon.)

Everything that goes after these five columns, yoma, yomi, yomu, yome, yomo, aren't part of the verb. They are suffixes. They're jodoushi and other auxiliaries.

For example, yoma~ plus the ~nai jodoushi forms yomanai, the negative form, while yome~ plus the ~ba jodoushi forms yomeba, the conditional form, and yomi~ plus the ~tai jodoushi forms yomitai, the desiderative form.

So far so good.

But then comes the ~eru suffix of potential verbs. It doesn't attach to ma-mi-mu-me-mo, it attaches to the m consonant, to form yomeru.

Since you can't divide yomeru 読める into yom~ よm~ and ~eru ~eる using only Japanese characters, it becomes impossible to explain this conjugation the same way you can explain the other conjugations in traditional Japanese grammar.

So the ~eru isn't called a jodoushi, and yomeru isn't called a verb form.

But wait, why can't you just say that this ~eru is actually just ~ru attached to yome~? Because there was yomeba, and nobody said it was yom~ plus ~eba. Why can't we just do that? What's the difference between yomeru and yomeba?

The difference is that even if yomeba is yom~ plus ~eba, you still have the ~ba sticking out. So you can say that this ~ba ~ば means the conditional function. Meanwhile, in yomeru, the thing that means the potential function is the ~e~ vowel, and we can't isolate that in Japanese writing.

Observe: yomeru is "able to read," while yomenai is "not able to read." So the "able to read" part remains the same even if you replace ~ru by ~nai. Therefore, ~ru doesn't have anything to do with it, it's only there to make the thing a verb.

If yom~ represents "to read," and ~ru doesn't matter, the only thing left to mean "able to" is the ~e~ vowel. And that screws everything up.

As you can see, potential verbs are basically a verb form. They just aren't a verb form because the Japanese language doesn't like it being a verb form, so it isn't. But everybody calls it a verb form, and absolutely nobody cares about whether it's technically a verb form or not.

But if potential verbs, kanou doushi 可能動詞, aren't the potential form, kanoukei 可能形, then what is the potential form of verbs? Where was it hiding all the time?

The actual potential form of godan verbs and ichidan verbs is identical to the passive form.
  • yomareru
    To be read. (passive.)
    To be able to read. (potential.)
  • taberareru
    To be eaten. (passive.)
    To be able to eat. (potential.)

Since this ambiguity is confusing, people came up with other ways to say the potential in order to avoid confusion:

These words, yomeru, tabereru, only mean the potential, they don't mean the passive, so now you have unambiguous ways to say the potential.

But now that you have unambiguous ways to say the potential, why would you use the ambiguous ways to say the potential? Indeed, you wouldn't. There's no point in doing that.

That's why the potential verb is overwhelmingly preferred, and nobody uses the ambiguous potential form.

When people want to use the potential they say yomeru, therefore, the word yomareru never gets used as the potential, because that would be confusing, so it only gets used as the passive, and this whole process sort of makes yomareru become unambiguous, too.

That's how you get people to think that yomareru is only passive, and that yomeru is the potential form. Because that's just how it works in practice.


Etymologically, the exact origin of kanou doushi is still unclear.[可能動詞 - 精選版 日本国語大辞典 via, accesed 2019-11-28.]

There are three noteworthy theories about their origins:(三宅, 2016:2)
  1. It's a change of pronunciation of a yodan verb conjugated to its mizenkei, plus the ~reru jodoushi. Basically, yomareru getting abbreviated to yomeru by removing ~ar or something like that.(山田孝雄, 1936, etc. cited in 三宅, 2016:2)
  2. It's a change in pronunciation of a yodan verb conjugated to its ren'youkei, plus the ~eru ~得る hojo-doushi 補助動詞. Basically, yomi-eru 読み得る getting abbreviated to yomeru. (渋谷 1993, cited in 三宅, 2016:2)
  3. It's analogous to the relationship of intransitive shimo-nidan verbs and transitive yodan verbs, e.g. yomuru 読むる, yomeru 読める.(坂梨, 1969, etc. cited in 三宅, 2016:2)

According to Miyake 三宅 (2016), the third theory is the most correct. That is, yomeru doesn't come from yomareru, and it doesn't come from yomi-eru, it's just kind of related to yomuru.


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