不必
búbì · HSK 3
not have to
不 (not) + 必 (must) = not must = need not
不 negates and 必 means must/necessarily, so 不必 literally reads as not-must, i.e. there's no obligation. Compare 必须 (must) — flip the order and add 不 to cancel the requirement.
不 — single pictograph; bird flying upward
Originally a pictograph in oracle bone script, traditionally interpreted as a bird flying up toward the sky and unable to come down, suggesting negation or refusal. Over time it became the standard negation word in Chinese, used before verbs and adjectives to mean 'not'.
必 — heart 心 + slash 丿
Originally depicted a handle or marker driven through something, suggesting a fixed standard. The form was later reanalyzed as 心 (heart) with a stroke through it, reinforcing the sense of inner certainty. It came to mean 'must' or 'certainly'.