べきではないShould not, Must not , Ought not to

たほうがいい est utilisé pour donner un conseil ou faire une suggestion, souvent en exprimant une opinion subjective sur ce que le locuteur pense « être préférable ». C'est une tournure couramment utilisée dans les conversations quotidiennes. En revanche, べきではない a le sens opposé et est plus formel. Il exprime une attente ou une règle sur ce qui « ne devrait pas » être fait, plutôt qu'un simple avis personnel.

なくちゃ and なきゃ are casual ways to express obligation, similar to 'I need to…' or 'I have to…' in English. In contrast, べきではない has the opposite meaning—'should not' or 'ought not'—and is more formal. It conveys a sense of societal expectation or what is considered proper, rather than reflecting the speaker's immediate or personal needs.

べき expresses strong obligation or moral judgment, as in doing something because it is right or proper, e.g. 約束は守るべきだ ('You should keep your promises.') べきではない is the negative form, used to advise against actions considered wrong or inappropriate, e.g. 人を見た目で判断すべきではない ('You shouldn't judge people by appearances.')

ことだ suggests what one should do as advice or a general guideline, e.g. 無理をしないことだ ('You should take it easy.') べきではない expresses the opposite, indicating what one should not do based on moral or social expectations, e.g. 人を見た目で判断すべきではない ('You shouldn't judge people by appearances.')

ものだ expresses general or societal expectations, e.g. 子どもは早く寝るものだ ('Children are supposed to go to bed early.') べきではない carries the opposite nuance, conveying that one should not do something based on moral or social reasoning, e.g. 人を見た目で判断すべきではない ('You shouldn't judge people by appearances.')

はずだ expresses an assumption or expectation based on reason or context, e.g. 雨が降るはずだ ('It should rain.'). In contrast, べきではない expresses a strong sense of moral or social obligation not to do something, e.g. 嘘をつくべきではない ('You shouldn't lie.').

These are opposites: なければならない 'must' vs. べきではない 'should not'. The former suggests a rule or necessity; the latter implies social or moral advice, e.g. 行かなければならない ('You must go.') as compared to 行くべきではない ('You ought not to / shouldn't go.').

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.').

てはいけない expresses prohibition, meaning something 'must not' or 'cannot' be done. In contrast, べきではない suggests that something 'should not' be done, often implying it's improper or that there's a better option. While both express negative recommendations, てはいけない is more authoritative and used for rules, whereas べきではない carries a more subjective nuance.

ないほうがいい is used to advise or suggest not doing something, similar to 'You shouldn't…' It is a common expression that reflects the speaker's personal or subjective opinion. べき can carry a similar meaning but is more formal, with a nuance of stating what one 'ought not to' or 'should not' do based on social norms or what is considered proper, rather than personal advice.

～と言っても typically qualifies or corrects an impression based on a previous statement, while ～というのは explains or defines something more directly. For example, 忙しいと言っても一日中じゃない ('I say I'm busy, but not all day') vs. 留学というのは海外の学校で勉強することです ('What we call study abroad means studying at a school in a foreign country').