Used to introduce a phrase or clause contrasting with what has already been mentioned. conjunction
She was tired, but she decided to continue working.
I want to go to the party, but I have to study for my exams.
Used to indicate the impossibility of anything other than what is being stated. preposition
There is nothing but sand in the desert.
He did nothing but complain all day.
Except; apart from; other than. preposition
Everyone but John was present at the meeting.
I would have called, but I lost my phone.
An objection or argument against something. noun
He had no buts about joining the team.
There are always buts when it comes to making big decisions.
Merely; only. adverb
He is but a child.
It was but a small error.