used to introduce a phrase or clause contrasting with what has already been mentioned

he stumbled but didn't fall

this is one principle, but it is not the only one

the food is cheap but delicious

the problem is not that they are cutting down trees, but that they are doing it in a predatory way

used to indicate the impossibility of anything other than what is being stated

one cannot but sympathize

there was nothing they could do but swallow their pride

they had no alternative but to follow

used to introduce a response expressing a feeling such as surprise or anger

but that's an incredible saving!

but why?

used after an expression of apology for what one is about to say

I'm sorry, but I can't pay you

without it being the case that

it never rains but it pours

except; apart from; other than

we were never anything but poor

supply currently exceeds demand in all but the most rural areas

the last but one

no more than; only

he is but a shadow of his former self

choose from a colourful array of mango, starfruit, and raspberries, to name but a few

(used at the end of a sentence) though; however

he was a nice bloke but

an argument against something; an objection

no buts—just get out of here

as with all these proposals, ifs and buts abound

an outer room, especially in a two-roomed cottage