Are there clear definitions for Japanese verb “roots,” “bases,” and “stems”? In books, online, and in classes, I encounter conflicting definitions, as described below.

ROOTS https://www.tofugu.com/japanese-grammar/verb-conjugation-groups/, accessed 6 Sept. 2022, defines “root” of both godan and ichidan verbs as “the part of the verb that (almost always) remains the same when the verb is conjugated. [Re.] 聞く… The part that remains the same in all the conjugations shown is kik, so it is the root.” The NihonShock website, https://nihonshock.com/2013/09/the-bases-of-japanese-verbs/, accessed 6 Sept. 2022, defines roots similarly: 上一段活用動詞 (見る, 用いる, Etc.) (roots end in i-) 下一段活用動詞 (食べる, 求める, Etc.) (roots end in e-) 五段活用動詞   (買う, 待つ, Etc.) (roots end in consonants) サ変活用動詞  (する)   (root is s-) カ変活用動詞    (来る)  (root is k-) However, as noted below, some people define this form as the verb ”base” or “stem.” Intensive Course in Japanese, Elementary, v. 3, from the Japanese Language Promotion Center, 1970, p. 47, says that for godan verbs, “the final syllable of the verb root takes the following different forms: かく kaku ki ku ka ko ke…” Yet a few pages earlier it states that the “stem” of かく is かき.

BASES Some say bases are synonymous with stems, but seem to define stems differently. For example, https://www.wasabi-jpn.com/japanese-grammar/japanese-verbs-u-verbs-and-ru-verbs-and-conjugation/, accessed 6 Sept. 2022, says: “Japanese verbs always contain two parts: a verb base and a suffix. Grammatically, verb bases are called ‘stems.’ … 見る, the stem is “mi” and the suffix is ‘ru.’ ” Since what precedes godan suffixes changes, this author must conceive five godan bases/stems. Similarly, the NihonShock website refers to a “simplified 7 base system”: ~A  動か 食べ し(する) こ(来る) ~I  動き 食べ し き ~U  動く 食べる する 来る ~E  動け 食べれ すれ くれ ~OU 動こう 食べよう しよう 来よう ~TE 動いて 食べて して きて ~TA 動いた 食べた した きた Under the heading Verb Bases, Wikipedia states, “Conjugable words … are traditionally considered to have six possible conjugational stems or bases (活用形, katsuyōkei, literally "conjugation forms") . …Verb bases function as the necessary stem forms to which inflectional suffixes attach. …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 る (ru) kana.” A former teacher told me that the verb base and stem are different. She said that the base is created by removing う from the dictionary form. “For example, with 行く, remove う. Just "ik" remains; it is the verb base.” Others would call that form a "root."

STEMS Many sources seem to agree that godan “stems” are formed by changing the final kana of a verb’s dictionary form to the associated kana ending in い (だす→ だし). Others create the same “stem” by removing –ます from the polite non-past affirmative form (Genki, 2nd ed., v. 1, pp. 151, 254). These sources do not mention godan forms such as ださ– or だせ– in their “stem” definitions, leaving it unclear whether these sources consider only –ます stems to be “stems.” (These sources say that ichidan stems are formed by removing –る from the dictionary form [たべる → たべ] ). Naganuma’s Basic Japanese Course: Grammar and Glossary, rev. ed., 1970, p. 23 specifies that the stem of godan verbs “ends in five different vowels or a combination of a consonant and vowels in the order of a, i,u, e, and o.” But the book almost immediately continues by referring to these five forms as Base I, Base II, etc., apparently considering “stem” and “base” to be synonyms. Meanwhile https://www.kanshudo.com/grammar/stem, accessed 6 Sept. 2022, says, “The term 'verb stem', also known as 'masu stem', … refers to the base part of the verb…. The easiest way to identify the stem … is to remove the ‘ます’…. The part of the verb that remains is the verb stem.” So this source also equates “base” and “stem,” but restricts its definition of stem to the –ます stem. The Complete Japanese Verb Guide by The Hiroo Japanese Center, 1989 and ‘91, pp. 10, 11, says that dropping the final う from the dictionary form of godan verbs (and the final るof ichidan verbs) creates their stems. As noted above, this is how some sources define “root.” Intensive Course in Japanese, Elementary, v. 3, 1970, pp. 40-48, agrees that a verb stem is “that part of a verb which always remains the same,” but then shows many “stems” that change (かき from かく, はなし from はなす). Wikipedia begins, “[T]he verb stem remains invariant among all conjugations” but continues, “The conjugational stem can span all five rows of the gojūon kana table.” In that case, the stem cannot remain invariant; and, as noted above, Wikipedia equates “stems” with “bases.”
Probably numerous additional citations could be added, but you can see the confusion. Are these apparently conflicting definitions because: • There are no precise definitions, causing people to deconstruct verbs by different systems? • Terms vary with the background of the author and/or perceived students/readers? • Some definitions simply are not worded well? I would be very appreciative of clarity!

  • This seems like largely a consequence of trying to map Western linguistic terminology onto a language with grammar - and phonetics - that just don't work the same way. I don't think it's a particularly useful question; arguing over the terminology doesn't help with understanding how the grammar actually works. Commented Jun 9, 2023 at 5:52
  • I was not "arguing' anything. As a fairly novice learner, I was asking a question so that I can better understand Japanese grammar. And, for the record, I still do not understand whether each of those terms has a clearly defined meaning.
    – NattoYum
    Commented Jun 10, 2023 at 12:45

1 Answer 1


In short, in the context of verb conjugation in Japanese, it seems base (語基) is the right word.

Note that this is just the result of googling and may contain errors.

According to this, the following is the general definitions (some controversies aside).

  • Roots are monomorphemic and have no lexical meaning. ("lexical meaning" should be the same as "meaning" in the ordinary sense, see comment.)
  • A stem must have lexical meaning and may contain derivational affixes.
  • A base is a form to which an affix may be adjoined. As such, it has no lexical meaning.
  • All roots are bases, but not all bases are roots.

Just taking an example from Wikipedia, 横切る's non-conjugating part contains 横切, which is not monomorphemic and can't be regarded as a root. Also, at the same time 横切 does not have a lexical meaning, it is not a stem either.

Now at this point already it is easy to see that there are some ambiguities around what is regarded as 'having a lexical meaning' - it should be possible to argue 横切 has a lexical meaning.

But anyway as long as one follows the definitions above, stem/root are misnomers in referring to non-conjugating parts in Japanese verbs because they are generally non-monomorphemic and don't have lexical meanings.

I think there are a few source of confusion. (The root cause may be applying linguistic notions from Western languages to Japanese.

(1) what is regarded as "non-conjugating" in Japanese verbs.

According to this pdf, there are two theories on what constitutes a 語幹 in Japanese verbs. One says it has multiple forms (1) and the other say there is only one (2). Taking an example from the pdf, the following is difference. Consider 貸す:

  1. Kas-u, Kasi-masu, Kasa-naide ...
  2. Kas-u, Kas-i-masu, Kas-a-nai

Following theory 1, kas/kasi/.. are all 語幹/語基. Theory 2 says it is kas. (What is more confusing, I believe school grammar teaches 語幹 of 貸す is ka.)

(2) the term 語幹.

It should correspond to stem, but literally speaking it means word trunk. I don't know the history, but it may have been in use before all those linguistic terms became common.

Either way, it looks plausible to me that 語幹 was and is used just because it is common. 語基 is a technical term and not understood outside linguistic circles. And because of these authors of Japanese text book tend to use stem, possibly unaware of difference among those terms (I have no evidence for this, of course).

  • I think your answer could be improved by explaining what "lexical meaning" means. Commented Sep 8, 2022 at 16:37
  • Thank you for your answer. I went to the the first link that you cited, but it seems to be about English-language verbs. I will look at the other references (as my question indicated, I did consult Wikipedia), but am wary of trying to apply to Japanese grammar information that applies to very different languages. I will look further into the information you provided.
    – NattoYum
    Commented Sep 8, 2022 at 17:37
  • @EiríkrÚtlendi I think it is more or less simply the ordinary meaning (e.g this ). And I believe it is impossible to pin down what it means to have a meaning (depending on the type of definition aimed at).
    – sundowner
    Commented Sep 8, 2022 at 22:27
  • @NattoYum I don't think JP linguistics deviates a lot from English Linguistics. Anyway, in the pdf I linked, an expert material uses the word 語基, which suggests it is the right word (which makes sense because base is something that can be turned into word by putting affixes.) Discrepancies you mention in the question result from either (1) JP grammar writers are not that careful about the terminology (this is my opinion) or (2) they have different opinions on those morphological notions.
    – sundowner
    Commented Sep 8, 2022 at 22:35
  • 1
    @sundowner, if you are using "lexical meaning" to just mean "meaning", I suggest that you remove the word "lexical", as that makes the text more difficult to understand. Commented Sep 9, 2022 at 16:58

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .