なければいけないMust do, Have to do

Both express obligation ('must do' or 'have to do') with a nuance of necessity. 行かねばならない and 行かなければいけない both express an obligation to go, and while なければいけない is already formal, ねばならない is even more formal and old-fashioned, often seen in academic or historical contexts. In daily speech, the contracted form なきゃ is more common than either.

なくてはいけない and なければいけない express obligation or necessity, saying something 'must' or 'needs to' be done. They are equivalent in meaning, with the only difference being that the なければ version is slightly more formal, though the difference is not highly significant. Note that in casual speech, these forms are often shortened to なくちゃ and なきゃ, respectively.

なくてはならない and なければいけない express obligation, meaning something 'must' or 'needs' to be done. The two forms are equivalent. The level of formality is similar, with なければ being slightly more formal than なくては and ならない being slightly more formal than いけない. The parts are interchangeable, and in casual speech, these forms are often shortened to なくちゃ and なきゃ, respectively.

Both なくちゃ・なきゃ and なければいけない express obligation or necessity, meaning something 'must' or 'needs to' be done. なければいけない is more formal and often appears in writing or official contexts, while なくちゃ・なきゃ are casual contractions (of なくては and なければ) used in everyday speech with friends and family.

These express contrasting meanings: なければいけない 'must' vs. べきではない 'should not'. The former implies necessity or rule, while the latter carries a tone of moral or social advice, e.g. 行かなければいけない ('You must go.') vs. 行くべきではない ('You shouldn't go.').

These are opposites: なければいけない expresses obligation (i.e. 'must'), while てはならない means prohibition (i.e. 'must not'). For example, 行かなければいけない ('You must go.') vs. 行ってはならない ('You must not go.'). Both are formal and common in writing or structured speech, while in conversation casual forms like なきゃ and ちゃ are more common.

てはいけない is used to express prohibition, meaning that something 'must not' or 'cannot' be done. In contrast, なければいけない expresses obligation, something 'must' be done. These forms can be tricky for learners, as なければいけない is negative in form but means 'must' (literally, 'it's not good if you don't'), while てはいけない is affirmative in form but means 'must not' (literally, 'it's not good if you do').

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).'.

These two patterns both express obligation (i.e. 'must do' or 'have to do'). For example, 行かなければならない and 行かなければいけない both express an obligation to go, but the ならない version is slightly more formal and found more often in writing. In everyday conversation, contractions like なきゃ (e.g. 行かなきゃ) are more common.