但是, 可是 and 不过 - how to know which one to use?
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.