べきMust, Should , Ought to

たほうがいい is used to give advice or make a suggestion, often expressing the speaker's subjective opinion on what they believe would be better. It's commonly used in everyday conversation. べき has a similar meaning, but is more formal and has a stronger nuance of expectation about what 'should' be done, rather than a personal opinion.

ないほうがいい is used to advise against doing something, similar 'You shouldn't…' in English. It is a common expression that reflects the speaker's personal or subjective opinion. べき has the opposite meaning ('You should,') and is more formal. It carries the nuance of stating what 'ought to' be done based on social norms, rather than giving personal judgment or advice.

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.')

Both expressions are similar in that they are both derived from the classical Japanese べし and relate to expectations, but they differ in precise meaning. べく typically expresses an action performed for a particular purpose, e.g. 上達すべく毎日練習しています ('I practice every day in hopes of getting better.'), while べき expresses a societal expectation in the sense of saying that something is how it 'should' be, e.g. 言いたいことがある時は本人に言うべきです ('When you have something to say, you should tell the person concerned.')

Both express what one 'should' do, but with different nuance. べき reflects personal or moral judgment, e.g. 約束は守るべきだ ('You should keep your promises.') ものだ conveys social or cultural expectations, e.g. 子どもは早く寝るものだ ('Children are supposed to go to bed early.')

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.').

Both express obligation, but differ in tone. ことだ is used to offer advice or general suggestions, e.g. 無理をしないことだ ('You should take it easy.') べき is stronger, implying moral or logical necessity, e.g. 約束は守るべきだ ('You should keep your promises.')

はずだ and べき can both be translated as 'should', but they differ in nuance. はずだ expresses an expectation based on evidence or reasoning, like 明日来るはずだ ('He should come tomorrow.'). In contrast, べき expresses obligation or social correctness, as in 来るべきだ ('You should come.').