1. We use BUT to link contrasting items which are the same grammatical type.

a) I have bought a new car but I still haven’t sold the older one. (joining two clauses)
b) The hotel was inexpensive but very comfortable. (joining two adjectives)
c) Quickly but silently he ran out of the house. (joining two adverbs)

NOTE-I: We can’t use HOWEVER as a conjunction instead of BUT to connect words and phrases; e.g.

INCORRECT: This dress is expensive however beautiful.
CORRECT: This dress is expensive but beautiful.

NOTE-II: BUT & HOWEVER

We can also use HOWEVER in the meaning of BUT i.e. when you are adding a comment that contrast with what has just been said, but HOWEVER can’t be used as a conjunction when used like this. It then generally starts a new sentence or clause; e.g.

Some of the food crops failed. However, the cotton did quite well.

INCORRECT: Ravi always cooks dinner, however I usually wash up afterwards.
CORRECT: Ravi always cooks dinner. However, I usually wash up afterwards. (or Ravi always cooks dinner but I usually wash up afterwards.)

NOTE-III: We use objective pronouns (me, you, him, us, etc.) after BUT even in subject position; e.g.

a) Everybody but me has finished work.
b) No one but him would get a job like that.

2. But For

BUT FOR = Were it not for. BUT FOR is used to introduce the reason why something didn’t happen; e.g.

a) But for the traffic, I would have reached half an hour early. (The traffic was very heavy – if it was normal, I’d have reached here half an hour early.)
b) I would have reached here on time but for the weather. (means I could not reach on time because of the weather)

3. All But

ALL BUT = almost completely; I had all but finished the letter when the computer crashed and I lost it all.

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