是否
shìfǒu · HSK 4
whether or not
是否 = is + not; literally 'is-or-isn't', asking whether something holds
是 means 'is/yes' and 否 means 'not/no'; pairing the two opposites forms a yes-no question marker, like English 'whether or not'. Common in formal writing and questions about truth or possibility.
是 — sun 日 + 正 (correct/upright)
Originally a compound suggesting 'the sun 日 directly overhead'—straight, correct, true. From this concrete sense of 'right' or 'this very thing,' 是 came to mean 'this' as a demonstrative, and later the modern copula 'to be / is.' The 'correct' meaning survives in words like 是非 (right and wrong).