但是 (dàn shì) is a coordinating conjunction meaning 'but' or 'however'. It connects two contrasting ideas or clauses — the first clause presents a fact, expectation, or situation, and the second introduces an unexpected or opposing detail. Though composed of two characters — 但 (dàn), meaning 'only' or 'merely', and 是 (shì), meaning 'is' or 'to be' — together they function as a single grammatical unit with no literal connection to their individual meanings. It is neutral in register and widely used in both spoken and written Chinese.

But unlike English 'but', 但是 typically appears at the beginning of the second clause (not mid-sentence), and it must be followed by a complete clause — never just a noun or adjective alone. It often follows a comma when joining independent clauses, and it’s frequently paired with a contrastive adverb like 也 (yě, 'also') or 还是 (hái shì, 'still') in the second clause to strengthen the contrast.