凡是
fánshì · HSK 6
whatever
凡 (every/ordinary) + 是 (is) = whatever is, all that is
凡 means every/all/ordinary, and 是 means is/to be. Together 凡是 literally reads as every-that-is, which maps onto whatever or any case where something holds true.
凡 — 几 enclosing a dot 丶
凡 originally depicted a flat tray or sail-like surface, shown as a frame with a small mark inside. From the idea of a plain, common container, it shifted to mean 'ordinary' or 'all in general'. The modern shape keeps the simple frame but no longer resembles a tray.
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).