Verb categories in Japanese

Ichidan (一段いちだん) verbs, also known as -ru verbs, always end in either -iru or -eru. The final る drops in many conjugations.

Models:

• 食たべる
  The final る drops in the many conjugations, and the potential and passive are identical. There are two alternative forms for the positive plain imperative: 食たべよ is more common in writing, and 食たべろ is colloquial.

Godan (五段ごだん) verbs, also known as -u verbs, can end in any of the following letters: う・く・ぐ・す・つ・ぬ・ぶ・む・る. These verbs have different sound changes in the past tense and -te form depending on their final letter, and they are grouped according to this into different verb models for each possible final letter.

Models:

• 買かう
  In past and -te forms the final う (u) becomes って, った, e.g. 買かって, 買かった.
• 書かく
  In past and -te forms the final く becomes いて, いた, e.g. 書かいて, 書かいた .
• 泳およぐ
  In past and -te forms the final ぐ becomes いで, いだ, e.g. 泳およいで, 泳およいだ.
• 指さす
  In past and -te forms the final す becomes して, した, e.g. 指さして, 指さした.
• 待まつ
  In past and -te forms the final つ becomes って, った, e.g. 待まって, 待まった
• 死しぬ
  In past and -te forms the final ぬ becomes んで, んだ, e.g. 死しんで, 死しんだ. This model is rare; the only word in common use in this model is 死しぬ “die”.
• 呼よぶ
  In past and -te forms the final ぶ becomes んで, んだ, e.g. 呼よんで, 呼よんだ.
• 飲のむ
  In past and -te forms the final む becomes んで, んだ, e.g. 飲のんで, 飲のんだ.
• 入はいる
  In past and -te forms the final る becomes って, った, e.g. 入はいって, 入はいった.

Suru (する) verbs end in the auxiliary verb する “do”, often formed by adding する after a noun to turn it into a verb, such as 勉べん強きょう “study (noun)”, 勉べん強きょうする “study (verb)”.

Models:

• する
  This model includes the verb する itself as well as most verbs formed with the auxiliary する. It conjugates differently than ichidan and godan verbs, with forms like negative しない, past した, causative させる and passive される. It is replaced with the verb できる “to be able to” in potential forms.
• 愛あいする
  This model is used for most verbs consisting of a single kanji character plus the auxiliary する. Its conjugation differs from the model する in potential forms, where it ends with conjugations of the suffix 〜せる instead of できる.
• 接せっする
  This model is used for verbs consisting of a single kanji character plus the auxiliary する when the kanji’s reading ends in small っ. Its conjugation differs slightly from the model 愛あいする in potential, passive, and causative forms.
• 禁きんずる
  These verbs are alternates of regular ichidan verbs ending in じる, e.g. 禁きんずる alternates with 禁きんじる. These conjugate like their alternates except in the present plain and -eba conditional forms.

There are a handful of verbs in Japanese with irregular conjugations that do not fit into the previous categories.

Models:

• だ
  The copula だ “be, is” has an irregular conjugation that is different than most Japanese verbs. In some conjugations there are alternate forms with では (more formal) and じゃ (more colloquial), e.g. in present negative ではない alternates with じゃない “is not”.
• ある
  The verb ある “exist, have, be” becomes ない in the negative present, and similarly in other negative conjugations.
• 有ある
  This is an alternate spelling of the verb ある, and it conjugates in the same manner. In negative conjugations it may be written with the kanji 無ない. This spelling emphasizes the possessive meaning of the verb (“have”), while the spelling 在ある emphasizes the verb’s meaning of existence (“be located, exist”).
• 在ある
  This is an alternate spelling of the verb ある, and it conjugates in the same manner. In negative conjugations it may be written with the kanji 無ない. This spelling emphasizes the verb’s meaning of existence (“be located, exist”), while the spelling 有ある emphasizes the possessive meaning of the verb (“have”).
• 来くる
  The verb 来くる “come” generally conjugates like an ichidan verb, but its kanji has a different pronunciation in different conjugations, e.g. 来きた, 来こられる. It also has the irregular imperative form 来こい.
• 行いく
  The verb 行いく “go” conjugates similarly to the godan model 書かく, except that its ending く becomes っ in -te form and past tense, e.g. 行いって, 行いった.
• くれる
  The verb くれる “give, do for someone” conjugates like other ichidan verbs except for its irregular imperative form くれ.
• なさる
  A few honorific verbs like なさる have this irregular conjugation model. They conjugate similarly to godan verbs ending in る, except that in polite forms and the positive imperative the る becomes い (e.g. なさいます).
• 問とう
  The two verbs 問とう and 請こう are slightly irregular godan verbs. They conjugate similarly to the 買かう model containing other verbs ending in う, but in past and -te forms the う stays unchanged, e.g. 問とうて, 問とうた.