Supplementary Comments on Japanese Verb Conjugations


Single-kanji 〜する verbs

Verbs consisting of a single kanji plus する, which are tagged as "vs-s" in JMdict/EDICT, have some variations in conjugation, especially in the plain negative form (and its derivations) and the potential forms. For example 愛する usually has a plain negative form of 愛さない, and 接する usually has a plain negative form of 接しない. These patterns extend to other conjugations using the negative Base; the negative て-form of 愛する is 愛さなくて, and of 接する is 接しなくて.

The possible reasons for this split in conjugation patterns are complex, and an interesting discussion of the topic can be found in this extract from the recently-published "Handbook of Japanese Lexicon and Word Formation". There also a lot of information in the Japanese Wikipedia page on サ行変格活用. It has also been observed that when there is a related 五段 verb (愛す in the case of 愛する) the 〜さない form tends to be used.

A similar division occurs with the potential forms of the verbs, with some such as 接する having a potential form of 接できる and others such as 愛する having mostly the 愛しうる/愛しえる form, however 愛できる is often used too. In general verbs which have a 〜さない negative form use the 〜しうる/しえる potential form, but there are exceptions such as 帰する where the negative is usually 帰さない and the potential is usually 帰できる.

There is a further group of single kanji plus する terms which are discussed in the reference mentioned above and which lie outside the group tagged as "vs-s". They include 恋する, 旅する and 値する, and can be treated as cases of a single-kanji noun with する. As they inflect the same as any other noun + する combination, they have the "vs-i" tag.


These two forms are often grouped together, as depending on context either can mean if or when in English. (McClure [below] devotes 10 pages to discussing the nuances.) To quote some examples from McClure:

If/when the President goes by, I will wave my flag.

The President may or may not be scheduled to go by. I won't wave my flag until he is going by. This sentence emphasises the order of events.

If the President goes by, I will wave my flag.

The President may or may not go by. If he actually does appear, I will wave my flag. The sentence makes clear the conditions under which flag-waving will in fact occur.

If the President is going to go by, I will wave my flag.

Given that the President is in fact going to drive by, I will wave my flag, perhaps starting immediately. The sequence of events is not relevant.

The -ますなら(ば) form has the rare alternative of -ませば.


The potentiality of a verb can be expressed in a couple of ways. One is to use 出来る (to be able to) as an auxiliary verb:

読むことができますか。 (Can you read [it]?)

If there is a close relationship between a direct object and the verb, the "をVこと" can be omitted, i.e.

mean the same.

The other is the potential form of the verb, typically constructed by adding られる to the base (一段 verbs) or adding る to a potential base formed by changing the last kana of the plain form from the う column to the え column (読む to 読める, 話す to 話せる, etc.) (五段 verbs). The potential form is itself an 一段 verb, and is an intransitive verb, generally taking the particle が instead of を.

この本を読むことが出来ますか。 (Can you read this book?)
この本が読めますか。(Can you read this book?)

The special class of single-kanji する verbs (害する, 愛する, etc.), which are marked as "vs-s" in WWWJDIC, have a potential form which ends in either しえる or しうる. The two are inter-changeable, (however just to complicate matters, the しうる form is not 五段, and does not inflect further; other inflections must be derived from the しえる form.) Some of these verbs also have a せる potential, which denotes capability to carry out something, and appears to be rather colloquial.


The causative form of a verb indicates that someone is made or allowed to perform the action. It is formed by adding させる to the base (一段 verbs) or せる to the negative base (五段 verbs)

There is an alternative form in which the せる is replaced by す. Thus there is 話さす instead of 話させる, etc. This form often has a nuance of more direct causation, for example 食べさす has a sense of feeding someone, rather than just making them eat.


I have used the label volitional/hortative to describe a set of verb forms which are often combined with the conjectural category (below) and called "presumptive". What I mean by volitional/hortative are the forms of verb that:

  1. express the speaker's intention, perhaps after some initial uncertainty, to do something (volition). Some duration of irresolution seems to be required to have passed before the speaker says anything in this meaning of the form, but it can be just a moment of hesitation, and the speaker is now ready to do it;
  2. express the speaker's attempts to get the addressee to join her/him in an action (exhorting).
  3. suggest that the speaker and addressee not take an action.

Formation usually involves the -おう/こう/.../よう and -ましょう inflections in affirmative statements. For example:

ビールを飲みましょう。 (Let's drink beer.)
食べましょう。 (Let's eat/We will eat/I will eat.)
電車で行きましょうか。 (Shall I/we go by train?)

As the -おう/こう/.../よう and -ましょう forms have no negative, the まい ending is sometimes used in the situation of expressing negative intention. It cannot be used to express a "let's not" situation, and in any case is a literary form and rarely seen at the ends of sentences, however it is fairly common in a dependent clause to show one's strong determination not to do something, as in

私は、彼女とは二度と会うまいと思う。 (I'm certainly not going to see her ever again!)
Often "Let's not do ..." is expressed by saying "Let's stop doing .." using 止める or 止す. E.g.
パーティーに行くのは止めましょう。 (Let's not go to the party.)

Another construction which means "let's decide to" or "let's try to" is verb+ことにしよう/しましょう or verb+ようにしよう/しましょう. For example:

名古屋までバスで行くことにしましょう。 (Let's [decide to] go as far as Nagoya by bus.)
This construction can be used where appropriate in negative sentences.
バスでは行かないことにしましょう。 (Let's [decide to] not go by bus.)

Note that that are many verbs where the volitional/hortative forms cannot be used in a meaningful way. One cannot say "午後に雨が降りましょう", for example. On the other hand, one might hear rockers on the stage yelling:

のってるか?今夜は燃えようぜ! (You guys getting in the mood? Let's burn it up tonight!)


This category of verb inflection is also often included in the broad presumptive category, and indeed there is some crossover between them. I have chosen to call it "conjectural", but it is also called "tentative" in some texts.

Strictly speaking, it is not a conjugation at all, as it usually involves the addition of the auxiliary だろう (formal: でしょう) to the informal form of the verb, both non-past and past. It expresses the speaker's belief that something may be the case, including past and future occurrence or non-occurrence of events of which he is not the author. Its closest English equivalent would be "probably", and when used in questions, it has a softening effect.

あのアパートは静かでしょう。 (That apartment is probably quiet.)
あの人は韓国人だろう。 (That person is probably Korean.)
大丈夫でしょうか。 (I wonder if it is all right.)
In the negative, the まい auxiliary, previously seen in the volitional category, can also be used to carry the sense of "probably not". As with the use of まい in the volitional category, this usage is strictly literary.
彼はもう英語を教えるまい。 (Most probably, he won't teach English any more.)

The -ないだろう form has the literary alternative form: なかろう.


The しろ imperative form of する has an literary alternative せよ.

Some Useful Links


William McClure: Using Japanese: a Guide to Contemporary Usage, Cambridge University Press.
Seiichi Makino and Michio Tsutsui: A Dictionary of Basic/Intermediate/Advanced(*) Japanese Grammar, The Japan Times. (3 books)
Taro Kageyama and Hideki Kishimoto (ed): Handbook of Japanese Lexicon and Word Formation, Walter de Gruyter GmbH & Co


My thanks to Bart Mathias and Shoji Yamazaki for their significant assistance with the verb conjugation option in WWWJDIC and with the preparation of these notes. Thanks also René Malenfant, Marcus Richert and the other JMdict editors for assistance with the investigation of single-kanji する verbs.