but作连词的多种用法

1. 但是，然而【用于连接两个意思相反或不同的单词或短语，注意书面语中but不能用于句首】
- Her books are fascinating but often rather disturbing.  
- "Has he got any experience?" "No, but he's keen to learn."

2. 可是【用于说明某事没有发生或不可能的原因]
- I'd like to go but I'm too busy. [意思是不会去]
- They would have married sooner, but they had to wait for her divorce. [意思是她若不离婚，他们就无法结婚]

3. 而是【用于否定句之后，强调第二句是真实的】
- He lied to the court not just once, but on many occasions.
- The purpose of the scheme is not to help the employees but to provide work for young people.

4. 除……以外【等同于except】
- What can we do but sit and wait?
- I had no choice but to accept the challenge.

but在口语情境中还有多种意思，见下一篇。