# 必要 vs 必須



## Looper

When to use which and when can I use both? What's the difference between the two?


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## frequency

必要 is more usual. 必須 could be specialist or technical. Formal? Not particularly. Often 必要 is safer than 必須 because it covers a wider range than 必須 can do.


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## SoLaTiDoberman

必要＝necessity, (adj)necessary
必須＝essence, (adj)essential


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## Flaminius

SoLaTiDoberman said:


> 必須＝essence, (adj)essential


I don't think 必須 is a noun.  Can you give an example that uses the word as a noun?  I have no problem with understanding 必要 as a noun in expressions like:
我が子の必要を満たす
必要に応じて支給する


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## SoLaTiDoberman

必須（ひっす）の意味 - goo国語辞書

必須なアイテム
成功のための必須の条件
必須アミノ酸


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## Flaminius

All three are legitimate Japanese expressions but do they use 必須 as a noun?


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## SoLaTiDoberman

If no, could you kindly show us the answer?


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## Flaminius

必須な is the adnominal form of an adjective which is 必須だ in the citation form.  Conjugation does not change parts of speech, so 必須な is also an adjective.

In 必須の, 必須 looks like a noun because one way of understanding 必須の is a noun governed by a postpositions*.  Postpositions govern a noun (or a noun phrase).  I wonder, however, how other postpositions can govern 必須.  Can it take _-ga_ and act as a subject?  I don't think it does, while 必要 can; as in 必要がないのに部屋にはいるな.  Can it take _-kara_ and express the reason of an action?  I don't think it does, while 必要 can; as in 法律上の必要から何通もの申請書を提出した.  If 必須 does not behave like a noun vis-à-vis other postpositions, it is at least less noun-like than 必要.  It may well be that 必須の is not noun phrase at all.  In fact, _-no_-marked forms are often used to supply adnominal forms of adjectives.  I once read a life of Nehru in translation and found ナショナリスチックの in a context which expected is ナショナリスティックな.  Since ナショナリスチック has never been a noun (in sense that it freely combines with postpositions), I tend to think what I found was an alternate form of the adnominal form ナショナリスティックな.  The same discussion can be applied to 必須の.

必須アミノ酸 uses 必須 as a modifier for アミノ酸.  必須 can be a noun as nouns can make compound nouns with other nouns.  To give you an example, 構造計算 takes two nouns and makes a new one.  There can be other possibilities.  It can be a Chinese adjective embedded in a Japanese noun compound.  Since no morphological markings are available for Chinese parts of speech, it may be permissible to determine the part of speech of a given Sino-Japanese word by its function.  Here, 必須 modifies a noun.  Thus, its part of speech may be an adjective.  Finally, it can be the stem of the adjective 必須な.  Japanese adjectives can modify a noun with their stems alone; e.g., たかやま, おおざけ.

If all the above is a tedious tangent, let me sum it up like this:
These examples use 必須 as a modifier of nouns. They are, therefore, inconclusive for the question if it is a noun.


*I am wont to use "postposition" for case markers as well as for postpositions that make noun phrases out of nouns.


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## SoLaTiDoberman

Thank you for the detailed explanation.

「必須」とは？意味や使い方を解説！ | 意味解説

How about these example sentences in the quote above?

俳句を詠む時は、季語は*必須*となりますから季節を間違えないようにしないと。
目標を達成する為にも、この試験に合格するのは*必須*となる。
Are they still not nouns? I don't know.

必須（ひっす）の意味 - goo国語辞書
必須(ひっしゅ)とは - 必須の読み方・Wiktionary日本語版（日本語カテゴリ） Weblio辞書

Dictionaries indicate that 必須 is *名詞* or *形容動詞*.

I agree that 必須 or even 必要 are almost always functioning as "adjectives."
So I wrote "necessary" "essential" and wrote "necessity" "essence" in the grey letters, even though they were not 必要な or 必須の.

It seemed to me that 必須 or 必要, instead of 必要な or 必須な, was defined as nouns in Japanese dictionaries, even when their usage were almost always restricted as "adjectives."

I understand what you explained.
I thought that it's a simple matter of the definition of Japanese grammar, which I didn't know much.
Thanks!

BTW, Google researches brought me the idea of the difference between 必須 and 必要.
They say that *必須 is more stronger in the meaning of the necessity than 必要*.
And an important thing for non-native Japanese learners is that they are usually/often used as "adjectives."


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## Flaminius

SoLaTiDoberman said:


> How about these example sentences in the quote  above? (Flam: It’s the source of your quotes below.)
> 
> 俳句を詠む時は、季語は*必須*となりますから季節を間違えないようにしないと。
> 目標を達成する為にも、この試験に合格するのは*必須*となる。


Some dictionaries analyze 必須と as the minimum unit for grammatical analysis.  大辞林3 says s.v. タリ活用:


> 「堂々と」など語尾に「と」をもつ副詞が動詞「あり」と結合してできたもので、語尾が「たら・たり（と）・たり・たる・たれ・たれ」と活用する。…〔口語には、この種の活用をする形容動詞はないが、連用形「－と」、連体形「－たる」の形だけはなお用いられるものがある。口語では、普通、「－と」（「堂々と・悠然と」の類）は副詞、「－たる」（「堂々たる・悠然たる」の類）は連体詞とする。



So, there are three ways to look at 必須と.
1. As the adverbial form of 必須たり, an adjective that conjugates in a paradigm largely obsolote now.
2. As a noun plus a postposition, combined to modify verbs.  Grammarians in the early 20th century would call it a 名詞連用修飾句.
3. As an adverb and you don’t want to open its belly to observe messy inwards.


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## SoLaTiDoberman

Interesting!
I wasn't able to think of "必須たり" as the dictionary form of "必須と."

*"必須 (and 必要？）are usually used as adjectives or adverbs."*


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