I learned that one way to form a "must" sentence is "negative verb + conditional + ダメ・ならない・いけない":

I mainly see two kinds of conditional used - the 仮定形 and と. For example



Then I thought, since と expresses a conditional that 100% will happen, like "if you drop an apple, it falls", does this mean that "must" sentences created with と express a stronger "must" than those created using the 仮定形?

  • 1
    I don't understand your question. But the two sentence mean the same. The first sentence is more colloquial and shorter version. The second one is more formal. There seems no difference about the strength between the two sentences.
    – user1118
    Aug 22, 2017 at 12:39

1 Answer 1


It's not really whether one is "stronger" than the other, but instead a more "standard" form. I find the following:


to be more common in instructional or written text, than say:


Part of the reason perhaps is prudence because it is quicker to say or understand, especially when you immediately need to call the listener's attention.

As a side note, I've seldom encountered the phrase


  • 2
    「なければダメ」 is SO common.
    – user4032
    Nov 26, 2017 at 12:04
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    Noted, but I DID say I personally only rarely come across it. I think of the なければなりません as a polite/formal set expression and ないと/なくちゃダメ as casual (perhaps just because it's quicker to say). But maybe that's just from my own personal experience.
    – keithmaxx
    Nov 30, 2017 at 1:44

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