But: Used to show a simple contrast between two ideas. It indicates opposition or contradiction without adding any element of surprise or unexpectedness.
Example: She is tired, but she keeps working.
Yet: Also shows contrast, but emphasizes an element of surprise or something unexpected. It's more formal and suggests that the second part of the sentence is unexpected given the first part.
Example: She is tired, yet she keeps working.
He tried hard, but he didn't succeed.
He tried hard, yet he didn't succeed.
but [bʌt]
yet [jɛt]