What's the best way to say that someone needs to do something, as in "5 English slangs you need to know"? I found some ways


Which is more correct or in what context should each be used? Is there a better way to say this?

1 Answer 1


First of all, one の is necessary between 五つ and 英語、and the first の is not necessary and the second の can be omitted such as 知る必要がある5つの英語スラング.

知る必要がある is "you need to know".

知らないといけない(知らなければならない) is "you must know".

知るべき is "you should know".

  • So, in addition to the difference in meaning, is there also a difference in politeness? Are these sentences polite or casual?
    – Yasushiki
    Jan 20, 2021 at 13:07
  • @Yasushiki They are normal how to say. If they changed to a polite form such as お知りになる必要がある5つの英語スラング, they would be awkward. Jan 20, 2021 at 14:06

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