How are conjugation endings called by Japanese linguists?


How are conjugation endings (たい, た, ない) called by Japanese linguists*?

Examples: 食べた _tabeta_ 'ate', 食べない _tabenai_ 'do not eat'

According to
[Wikipedia](https://ja.wikipedia.org/wiki/%E5%8A%A9%E5%8B%95%E8%A9%9E_\(%E5%9B%BD%E6%96%87%E6%B3%95\)),
and an electronic dictionary, it seems they are considered 助動詞 _jodōshi_.

I still wonder if they are not classified as other parts of speech (for
instance 助詞 _joshi_ ), or if they are considered
[suffixes](https://ja.wikipedia.org/wiki/%E6%8E%A5%E5%B0%BE%E8%BE%9E) (接尾辞
_setsubiji_ ).

It would be possible that they are directly referred as 活用形 _katsuyōkei_.

*By "Japanese linguists" I mean linguists who are Japanese, working in Japan, and producing textbooks such as those studied in schools; or scientific research published in Japanese, in Japanese journals.




You have answered your own question, but (食べ) **たい** , (食べ) **ない** , (食べ)
**た** , (食べ) **ます** and so on are almost always called 助動詞 in traditional
_国文法_ studied by
[国語学者/日本語学者](https://ja.wikipedia.org/wiki/%E6%97%A5%E6%9C%AC%E8%AA%9E%E5%AD%A6%E8%80%85)*
and taught by Japanese middle/high school teachers. These are always called
助動詞 in monolingual dictionaries, too. Importantly, these are words on their
own, and not part of a verb's conjugation form.

(* I personally hesitate to call them 言語学者 for a reason, but I won't go into
the details about it...)

For example, 書かない consists of two words, `書か` (未然形 of 書く) + `ない` (助動詞 for
negation). 書きたい is also two words, `書き` (連用形 of 書く) + `たい` (助動詞 for desire).
書いた is `書い` (another 連用形 of 書く) + `た` (助動詞 for past tense). 書きたくなかった has all
the four words, `書き` (連用形 of 書く) + `たく` (未然形 of たい) + `なかっ` (連用形 of ない) + `た`
(終止形 of た).

This is different from what you may have learned as a JSL (Japanese-as-a-
second-language) learner, but that's how the Japanese grammar is usually
taught and discussed in Japanese.

> It would be possible that they are directly referred as 活用形 katsuyōkei.

Indeed, if you're seeing only simple examples like 歩い **た** , it may be hard
to see how it's different from "walk **ed** ". The main reason these 助動詞 are
considered independent words is that they can be combined to say complex
things.

For example, 食べさせられたくなかった means "did-not-want-to-be-made-to-eat", but it's odd
to call something like this a "form" when it can be logically split into
smaller parts. According to 国文法, this is a "simple" combination of 6 words, 5
of which are 助動詞: `食べ` + `させ` (causation) + `られ` (passive) + `たく` (desire) +
`なかっ` (negation) + `た` (past).

書きませんでした is often introduced as a "form" (negative-polite-past-form) in JSL
textbooks, but this is just for the sake of convenience. The rules governing
助動詞 are a little too tricky for a beginner, so it's faster to learn them by
rote as a form at first.

For another thing, while there are a few irregular verbs in Japanese, their
irregularity does not cross word boundaries and affect the following 助動詞. For
example, 行く is a well-known irregular verb whose "past form" is not 行いた but
行った, but you can see the た part remains た. This is another reason why 助動詞 are
considered separate. In English, the past form of _go_ is _went_ , and it's
impossible to see two words in it.

> I still wonder if they are not classified as other parts of speech (for
> instance 助詞 joshi), or if they are considered suffixes (接尾辞 setsubiji).

助動詞 are clearly different from 助詞 (particles; を, が, へ, から, etc):

  * 助詞 usually follow 体言 (nouns), whereas 助動詞 usually follow 用言 (verbs and i-adjectives).
  * 助詞 never conjugate, whereas 助動詞 can conjugate by themselves. For example, たい and ない themselves conjugate like an ordinary i-adjective (たく, たかっ, たけれ; なく, なかっ, なけれ), allowing another 助動詞 to follow it.
  * In terms of purpose, 助詞 is closer to English prepositions ( _to_ , _of_ , _at_ , etc) while 助動詞 is closer to English auxiliary verbs ( _can_ , _should_ , _must_ , etc).

A 接尾辞 (suffix) forms another single word. For example, in English, "boy **s**
" is still one word, and "bright **en** " is still one word. However, a
Japanese 助動詞 is a bit too flexible to be called a part of a word, as described
above, and that's why they are not called suffixes.

Related:

  * [Auxiliary verbs in Japanese](https://japanese.stackexchange.com/q/63351/5010)
  * [Why Japanese verb has so many forms?](https://japanese.stackexchange.com/q/61902/5010)
  * [Do I have a good grasp on the basics of what the continuative form is?](https://japanese.stackexchange.com/q/65936/5010)
  * [Does "te-form" of a verb always include て/で? Why?](https://japanese.stackexchange.com/q/36310/5010)

( **EDIT** : Oh, I noticed [接尾辞 in Japanese
Wikipedia](https://ja.wikipedia.org/wiki/%E6%8E%A5%E5%B0%BE%E8%BE%9E) does not
agree with what I explained above. So this is one way where 国文法 and 言語学
differ... Whoever wrote this seems to think even が and は are suffixes based on
some linguistic theory, but I don't think those who adhere to 国文法 would
agree.)

