Comparing “què” and “kěshì / dànshì”
却 vs 可是 / 但是
How it works
All three can express contrast, but they work differently.
却 (què) is usually an adverb placed inside the sentence. It often highlights an unexpected contrast between expectation and reality.
可是 (kěshì) and 但是 (dànshì) are conjunction-like connectors that link two clauses more directly.
The difference
却 (què) = compact, internal contrast, often more refined
可是 (kěshì) = conversational contrast
但是 (dànshì) = neutral and common contrast, often slightly more formal than 可是 (kěshì)
Example sentences
他看起来很平静，心里却一直放不下这件事。
He looks calm, yet in his heart he still cannot let this matter go.
我明白你的意思，但是这个办法在现实中未必行得通。
I understand what you mean, but this method may not necessarily work in reality.
他不是没有能力，可是总在关键时刻缺乏决心。
It is not that he lacks ability, but he always lacks determination at crucial moments.
Key point
却 (què) is usually more elegant and more integrated into the sentence. 可是 (kěshì) sounds more spoken. 但是 (dànshì) is neutral and broadly usable.