It should be mentioned I can't read kanji, so please keep that in mind when answering

I've just encountered the verb [必要]{ひつよう}, in the Rosetta Stone sentence


Question 1: Does 必要 operate the same as 要ります? Is there a difference in what it implies, or is it like the english equivalent of need vs require, where the difference isn't meaning but context and which fits the sentence better?

Question 2: Can I use 必要 before and after が?
I.e. are these three sentences equally valid? Do they mean the same thing?:

  1. 私は [読]{よ}む [の・こと] が [要]{い}ります 

  2. 私は 読む 必要 が あります

  3. 私は 読む [の・こと] が 必要 です


In fact, 必要 is not a verb, but a noun. It can be an adjective if it is followed by な. As a noun, 必要 means "a necessity" or "a need". As an adjective, it means "necessary" or "needed".

そんなに高いパソコン買う必要ありますか? Is there a necessity to buy such an expensive computer?

たくさんの文献を読む必要がある。 There is a necessity to read a lot of literature.

ログインが必要です。 The login is a necessity.

必要な物 necessary things

But 要る / 要ります is a real verb, so the construction will be different:

パソコンが要ります。 I need a computer.

I would say that the meaning is quite similar, and that the main difference is their role in the sentence (verb, noun, adjective).

A slight difference about the meaning could be that 必要がある is more used in order to express an "external necessity" (that doesn't come from you), like a rule or a law. For instance, if you want to buy something, there is a necessity for you to have money. On the contrary, 要る can also express that you want something, so this is an "internal necessity" (that comes from you).

As @naruto said in the comments, the expression "を必要とする" ("require" / "call for") can also be found:

パソコンを必要とする。 This task requires a computer.

技術を必要とする分野 a field that requires skill

As @Chocolate♦ said in the comments, "読むことが要ります" would be understood but it sounds strange and is almost not used. Prefer other suggested alternatives.

  • 1
    That should be パソコンが要ります.
    – Angelos
    Aug 27 '15 at 14:43
  • 1
    And there's also パソコン必要とする.
    – naruto
    Aug 27 '15 at 15:00
  • @Nothingatall thank you for highlighting this. I fixed it.
    – RotS
    Aug 27 '15 at 15:18
  • 1
    '...and "verb+ことが要ります" are correct.' >> We don't say 読むことが要ります. If not use the word 必要, you'd say 読まないといけません, 読まなければいけません etc.
    – Chocolate
    Sep 9 '15 at 4:53
  • 3
    I think it's understandable but awkward, unnatural or sloppy. There's only 104 results on Google for "ことが要ります", only 1 for "読むことが要ります", and I wouldn't recommend learners to use it.
    – Chocolate
    Sep 9 '15 at 14:21

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