But if

unless.
- Chaucer.

See also: But

References in classic literature ?
"In the house," said the woman, bursting into tears; "but if it should happen to be in the road, and you ran over it, those great wheels would crush my darling to jelly.
"I've never heard of any," admitted the woman, "but if there were--"
But if these secret golden keys did seem to open in him his own secret golden treasuries, yet did his breath upon them prove but tarnishing.
But if you was to go to Europe you'd see a raft of 'em hopping around."
"But if thee mean'st it about myself, I've given up all thoughts as she can ever be my wife.
"If La Billardiere's place is given to Rabourdin I may be believed when I praise the superiority of his wife," replied des Lupeaulx, piqued by the minister's sarcasm; "but if Madame la Comtesse would be willing to judge for herself--"
But if one looks at men in all ways--are there many good ones left?
But if you want to know, we really have something in common."
"Oh, it is the saddest tense," sighed Rebecca with a little break in her voice; "nothing but IFS, IFS, IFS!
But if you listen carefully, you can just here a collective groan out there somewhere.
PR guru Max Clifford said Henson could build a massive fan base: "It's all ifs, buts and maybes but if he does really well, not just in terms of dancing on Strictly, but also in terms of personality, it will give him a massive shop window.
But if we end up with an Easter deluge, the fair could end up stuck there and, quite possibly, sinking.