How does ないと signify "must" in Japanese sometimes?

Question

So my language resources gave me this sentence, in many forms and I still cant understand where "must" comes from or the need to in the Japanese. It's frequent, and I'm assuming a grammar phrase with no literal translation, but mega confusing.

そろそろ恐怖心に立ち向かわないと行けないね。

Translated as "It's time for me to face my fears."

In this particular sentence, it's the added 行けない at the end that confuses the hell out of me, as my head is interpreting it as "must not".

More generally it's the use of these ないと and 行けない being paired I've seen used a lot which confuses me, as I only associate it with a negation as nai general meaning/use.

Thanks

Answer 1

First, yes, 〜ないといけない is a grammatical phrase, usually translated as "must" or "have to". Correspondingly, it will usually be written in hiragana rather than kanji.

Second, your confusion is totally natural; I think a lot of Japanese learners will come across constructions with a couple of negatives and a conditional in the mix and wonder how to parse it... But, there is some logic to this expression, and you can break it down a bit if you must for the sake of understanding it. The two things to look at are:

1) 〜ないと means "If (I) don't 〜", usually with a greater sense of importance/associated repercussions than its grammatical siblings なければ or なかったら.

2) While いけない can indeed mean "must not", it can (quite relatedly) mean something like "it's no good".

Therefore, perhaps you might prefer to unpick the complete phrase ないといけない as meaning "If I don't do it, it'll be no good - so logically, I must do it".

Hopefully, as you see/use the phrase more, it'll just click into place as its plainer translation of "must" or "have to", but that sort of explanation might help in the meantime.

Answer 2

-ないと doesn't indicate "must", but -ないといけない does (the 行 also usually wouldn't be written in kanji in this case, either). It's one of a few set phrases that just mean "must", and are pretty automatic when that's what you want to express. Some similar patterns that work the same way are:

• それをしないとならない
• それをしなくてはダメ

Instead of using -ないと, you can also use -なければ or -なくては. In the case of the ダメ expression I think I've only seen -なくては used.

The flavors are perhaps slightly different, especially with ダメ which is more forceful/blunt. I can't tell a difference between いけない and ならない (but I'm not native, either). But they're both just rattled off without thinking - no one's conscious of saying "If you do this it won't [go/do]", the feeling is exactly "you must do X". Except of course that the ダメ one is perhaps something more like "it would be unacceptable to fail to do X". Still a rote phrase, though.

See this post from Tae Kim's guide for more info.