besides : 着重于指另外还有。
- She won't mind if you're late - besides, it's hardly your fault.
- Do you play any other sports besides basketball?
but : 侧重指不包括在内。
- Eventually, all but one of them promised to come to his birthday party.
- He's anything but violent (= not violent in any way).
- I would have crashed the car but for your warning.
- This is the last episode but one (= one before the last) of the series.
- She's one of those guests who does nothing but complain.
- This car has been nothing but trouble - it's always breaking down!
except : 侧重于排除在外，从整体里减去。可与but换用，但语气较强。
- The museum is open daily except Monday(s).
- The government has few options except to keep interest rates high.
- It's cool and quiet everywhere except in the kitchen.
- Everyone was there except for Sally.
- There is nothing to indicate the building's past, except (for) the fireplace.
except for : 多用于在说明基本情况或对主要部分加以肯定，还引出相反的原因或细节，从而部分地修正前面的主要意思，含惋惜意味。
- Everyone was late, except for Richard.
- Apart from [ Except for] a few grammatical mistakes, this composition of yours is well written.
- I sold everything I owned except for my car and my books.
- She sipped the wine. Everything was hazy now, except for Nick's face.