Japanese verbs, like the verbs of many other languages, can be phonetically modified to change their purpose, nuance or meaning – a process known as conjugation. In Japanese, the beginning of a word (the stem) is preserved during conjugation, whilst the ending of the word is altered in some way to change the meaning (this is the inflectional suffix). Japanese verb conjugations are independent of person, number and gender (they do not depend on whether the subject is I, you, he, she, we, etc.); the conjugated forms can express meanings such as negation, present and past tense, volition, passive voice, causation, imperative and conditional mood, and ability. There are also special forms for conjunction with other verbs, and for combination with particles for additional meanings.
Japanese verbs have agglutinating properties: some of the conjugated forms are themselves conjugable verbs (or i-adjectives), which can result in several suffixes being strung together in a single verb form to express a combination of meanings.
Verb groups
For Japanese verbs, the verb stem remains invariant among all conjugations. However, conjugation patterns vary according to a verb's category. For example, and belong to different verb categories (godan and ichidan, respectively) and therefore follow different conjugation patterns. As such, knowing a verb's category is essential for conjugating Japanese verbs.
Japanese verbs can be allocated into three categories:
, also known as "Class‑5 verbs" , also known as "Class‑1 verbs" Irregular verbs, most notably: and
Verbs are conjugated from their "dictionary form", where the final kana is either removed or changed in some way. From a technical standpoint, verbs usually require a specific conjugational stem (see § Verb bases, below) for any given inflection or suffix. With godan verbs, the conjugational stem can span all five rows of the gojūon kana table (hence, the classification as a class‑5 verb). Ichidan verbs are simpler to conjugate: the final kana, which is always , is simply removed or replaced with the appropriate inflectional suffix. This means ichidan verb stems, in themselves, are valid conjugational stems which always end with the same kana (hence, the classification as a class‑1 verb).
This phenomenon can be observed by comparing conjugations of the two verb types, within the context of the gojūon table.
These forms are given here in hiragana for illustrative purposes; they would normally be written with kanji as , etc.
As visible above, the godan verb has a static verb stem, , and a dynamic conjugational stem which changes depending on the purpose: , , , and . Unlike godan verb stems, ichidan verb stems are also functional conjugational stems, with the final kana of the stem remaining static in all conjugations.
Verb bases
Conjugable words (verbs, i‑adjectives, and na‑adjectives) are traditionally considered to have six possible . However, as a result of the language evolving, historical sound shifts, and the post‑WWII spelling reforms, three additional sub‑bases have emerged for verbs (seen in the table below as the Potential, Volitional, and Euphonic bases). Meanwhile, verbs no longer differentiate between the and the bases (these bases are only distinguished for na‑adjectives in the modern language, see Japanese adjectives). Verb bases function as the necessary stem forms to which inflectional suffixes attach.
Verbs are named and listed in dictionaries according to their . This is also called the "plain form" (since this is the plain, non‑polite, non‑past conjugation), and it is the same as the modern , and the . The verb group (godan, ichidan, or irregular) determines how to derive any given conjugation base for the verb. With godan verbs, the base is derived by shifting the final kana along the respective vowel row of the gojūon kana table. With ichidan verbs, the base is derived by removing or replacing the final kana.
The table below illustrates the various verb bases across the verb groups, with the patterns starting from the dictionary form.