Overview
These four all push toward doing (or not doing) something, but they differ in where the pressure comes from and how personal or official it is. べきだ states a moral or social principle — “one ought to,” advice grounded in right and wrong. べきではない is its negative — “one ought not to.” こと issues an impersonal rule — the flat “must” of signs, notices, and printed instructions. ないと expresses a casual personal necessity — “I’ve gotta,” literally “if I don’t, it’s bad,” with the consequence left hanging. The shorthand for students: べきだ advises on principle, こと posts a rule, ないと is the everyday “gotta.” The entries below lead with a simple example, then a funny one, and draw the boundaries.
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