必

Core sense of something "fixed," spanning the range from subjective certainty to objective necessity. It may function as a prediction (certainty: "surely," "certainly," "will inevitably") or a requirement (necessity/imperative: "must," "shall," "is required to").

Functions as an adverbial modifier, almost exclusively preceding the verb or predicate. In the negative construction 不必, the meaning typically shifts from prohibition to a lack of necessity ("no need to" or "not required").

Contrast with 須 (xū): while both can mean "must," 必 leans toward an absolute requirement or inevitable result, whereas 須 often denotes a prerequisite. Contrast with 當 (dāng): 當 typically implies appropriateness, duty, or expectation ("ought to"), whereas 必 implies a stern demand or unavoidable conclusion.

The distinction between a confident prediction and a requirement depends on the author's posture (predicting a state of affairs vs. issuing an order). If 必 appears where a prerequisite marker like 須 would be expected, it suggests the author views the action as an unavoidable conclusion rather than a mere step in a process.