Character 必

It signals necessity or certainty; surrounding words decide. Chinese 必须/必須 states a requirement; 必然 marks inevitability. Japanese 必ず can express certainty or obligation.

Did 必 originally depict a weapon haft?

One account reads an early form as a weapon haft. The earliest attested ancestor appears in late Shang oracle-bone writing—ritual inscriptions on animal bones and turtle shells used to seek answers. The haft reading also occurs in Western Zhou bronze inscriptions. Under this account, 必 was borrowed for “must/certainly”; adding 木 formed 柲 for the physical haft. The modern shape is not a literal picture.