Editing Japanese grammar (section)

===Stem forms===
Conjugative suffixes and auxiliary verbs are attached to the stem forms of the affixee. In modern Japanese, there are six stem forms, ordered following from the {{transliteration|ja|-a, -i, -u, -e, -o}} endings that these forms have in {{nihongo|5-row|五段}} verbs (according to the {{lang|ja|あ、い、う、え、お}} collation order of Japanese), where terminal and attributive forms are the same for verbs (hence only 5 surface forms), but differ for nominals, notably {{transliteration|ja|na}}-nominals.
; {{nihongo|''Irrealis form''|未然形|mizenkei}} {{transliteration|ja|-a}} (and {{transliteration|ja|-ō}}): is used for plain negative (of verbs), causative and passive constructions. The most common use of this form is with the {{transliteration|ja|-nai}} auxiliary that turns verbs into their negative (predicate) form. (See Verbs below.) The {{transliteration|ja|-ō}} version is used for volitional expression and formed by a {{nihongo|euphonic change|音便|onbin}}.
; {{nihongo|''Continuative form''|連用形|ren'yōkei}} {{transliteration|ja|-i}}: is used in a linking role (a kind of [[serial verb construction]]). This is the most productive stem form, taking on a variety of endings and auxiliaries, and can even occur independently in a sense similar to the {{transliteration|ja|-te}} ending. This form is also used to negate adjectives.
; {{nihongo|''Terminal form''|終止形|shūshikei}} {{transliteration|ja|-u}}: is used at the ends of clauses in [[predicate (grammar)|predicate]] positions. This form is also variously known as {{nihongo|''plain form''|基本形|kihonkei}} or {{nihongo|''[[dictionary form]]''|辞書形|jishokei}} – it is the form that verbs are listed under in a dictionary.
; {{nihongo|''[[Attributive verb#Japanese|{{vanchor|Attributive form}}]]''|{{vanchor|連体形}}|rentaikei}} {{transliteration|ja|-u}}: is prefixed to nominals and is used to define or classify the noun, similar to a [[relative clause]] in English. In modern Japanese it is practically identical to the terminal form, except that verbs are generally not inflected for politeness; in old Japanese these forms differed. Further, {{transliteration|ja|na}}-nominals behave differently in terminal and attributive positions; see [[#Adjectival verbs and nouns|Adjectival verbs and nouns]], below.
; {{nihongo|''Hypothetical form''|仮定形|kateikei}} {{transliteration|ja|-e}}: is used for conditional and subjunctive forms, using the {{transliteration|ja|-ba}} ending.
; {{nihongo|''Imperative form''|命令形|meireikei}} {{transliteration|ja|-e}}: is used to turn verbs into commands. Adjectives do not have an imperative stem form.

The application of conjugative suffixes to stem forms follow certain {{nihongo|euphonic principles|音便|onbin}}.