Translation guide
The English phrase 'if not ...' is used to introduce a conditional negative, often as a warning, threat, or alternative. In Japanese, this is expressed through various conditional forms combined with negation, depending on the nuance and context.
Unless it rains, the event will be held.
Formal exception
To express that if something is not done, a negative consequence will follow. Often used in commands or strong suggestions.
A common colloquial pattern meaning 'if (you) don't ~, then ...'. The 'to' conditional implies a natural or inevitable consequence. Often used in casual speech.
If you don't hurry up, you'll be late.
If you don't study, you'll fail the exam.
The standard conditional form 'nakereba' meaning 'if not'. More formal and neutral than '~nai to'. Can be used in both spoken and written Japanese.
If you don't hurry, you won't make it in time.
Uses 'nara' conditional, often when the condition is based on the listener's intention or situation. 'If you're not going to do it, then...'
If you're not going, I won't go either.
To present a negative condition as an alternative or exception to a general statement. 'If not X, then Y' or 'unless'.
Means 'unless' or 'as long as not'. Stronger than simple conditional, emphasizing that the result holds true except under the stated condition.
Used to emphasize a statement by suggesting an extreme or obvious alternative. 'If that's not X, I don't know what is.'
A rhetorical phrase meaning 'if that's not X, what is?'. Used to strongly assert that something is definitely X.
In casual speech, 'if not...' can be used as a standalone phrase implying a threat or warning without stating the consequence. 'Or else!'
The trailing 'to' conditional without the result clause. Very common in casual warnings. Implies 'or else something bad will happen'.
All three express 'if not', but differ in nuance. ～ないと is casual and often implies a natural consequence or warning. ～なければ is the standard conditional, neutral and widely usable. ～ないなら is used when the condition is based on the listener's intention or situation, similar to 'if it's the case that you won't...'.
If I don't go, I'll get scolded. (natural consequence)
If you don't read the instructions, you won't understand how to use it.
If you're not going to eat it, please put it away.
The game will be held unless it rains.
I won't forgive him unless he apologizes.
The negative form of 'de aru' (to be). Used for 'if it is not X, then Y'. Often for nouns and na-adjectives.
If it's not him, no one can do this job.
If it's not quiet, I can't study.
If this isn't love, what is?
Literally 'it is nothing other than X'. A strong assertion that something is exactly X. Similar to 'if not X, then nothing'.
This is nothing short of a miracle.
If you don't do it properly... (or else).
If you don't hurry up...
The more formal 'nakereba' trailing off. Less common in casual speech but can be used for a slightly more polite or serious tone.
If you're not more careful...
If I don't go, there's no problem. (neutral condition)
If you're not going, I'll quit too. (based on your intention)
English 'if not' cannot be directly translated as もし～ない in most cases. Japanese uses integrated conditional forms like ～なければ or ～ないと. Using もし with a negative is possible but often sounds unnatural or overly tentative.
If I don't go, I'll call. (grammatical but もし is often omitted)