According to my dictionary, 但是, 可是 and 不过 all mean "but/however"? However are there any differences between them? Are there some cases, where one can be used but not another?
Check out this page: 3 ways to say 'but' in Chinese - difference between 不过 bù guò - 可是 kě shì - 但是 dàn shì.
That page says that:
- 不过 is softer.
- 可是 is usually associated with something unfortunate.
- 但是 is more formal and stronger.
Normally you can just use 但是. When you use them as "but/however", they are essentially the same. The only difference is the intensity of tone: 但是 is the strongest like "but", the other two are less strong, but still close to "but". There is 然而 which is usually translated as "however".
但是 is only used as "but", while 可是 and 不过 have various other usages.