ないとMust, Have to

なくちゃ, なきゃ, and なくてはいけない express obligation, meaning something 'must' or 'needs' to be done. なくてはいけない is more formal, while ないと (the negative form plus conditional と) is a casual alternative. While いけない can be replaced with ならない, ないと is usually used on it's own or followed by いけない or だめ, the more casual option.

Both ないと and なくちゃ・なきゃ express necessity or obligation in casual speech, similar to 'I have to' or 'I need to' in English. They are very close in meaning and formality, and are generally interchangeable in everyday conversation with little to no difference in nuance.

These expressions mean the same thing but differ in formality. ないと is used casually in speech, as in もう行かないと ('I need to go soon.'). なければいけない is more polite and suitable for formal contexts. Both mean 'I must (A).' or 'I have to (A).'.

Both express obligation, but differ in tone. ないと is casual and often shortened in speech, as in 行かないと ('I've got to go.'). なければならない is more formal, used in writing or polite conversation. Both convey the idea of needing to do something.

Les deux expressions ないと et なくてはならない indiquent une obligation ou une nécessité, signalant qu'il « faut » ou qu'on « doit » faire quelque chose. なくてはならない est plus formelle, tandis que ないと est une alternative plus décontractée. ないと peut se suffire à elle-même ou être suivie de いけない (plus formelle) ou だめ (plus décontractée), mais il est généralement déconseillé de l'utiliser avec le formel ならない.

ないと and べき both express a sense of necessity, but with different nuances. ないと focuses on immediate or practical obligation, like 行かないと ('I've got to go.'). べき expresses moral or logical duty, as in 行くべきだ ('You should go.').