A1
used to introduce an added statement, usually something that is different from what you have said before
Dictionary examples:
I want to sleep, but coffee says no. (0.0)
He's smart, but can't find his glasses. (0.0)
I can run fast, but only to food. (0.0)
She's not only a painter but also a writer. (19.8)
I think it's true, but then, I'm no expert. (22.3)
She's very hard-working but not very imaginative. (36.0)
You can invite Keith to the party, but please don't ask that friend of his. (42.6)