if

1. Supposing that, assuming that, in the circumstances that; used to introduce a condition that may be (or prove to be) either true or false.Examples: "if A then B else C"

2. Supposing that; used with past or past perfect subjunctive to indicate a counterfactual or hypothetical condition.Examples: "I wouldn't marry you if you were the last man on earth."; "You're finishing your chowder if you sit there all afernoon!"; "“Wait a minute!” said the girl: “I wouldn’t hurry by, if it was you that was coming out to be hung, the next time eight o’clock struck, Bill. I’d walk round and round the place till I dropped, if the snow was on the ground, and I hadn’t a shawl to cover me.”"excessiveusually

3. (sometimes proscribed) Whether; used to introduce a noun clause, an indirect question, that functions as the direct object of certain verbs.Examples: "I don't know if I want to go or not."; "Quoth Matthew, “ […] / She doubts if two and two make four, / […] ”"; "It is doubtful if the Victorian Londoner needed any warning, for the artful mobsmen, toolers, whizzers and dippers, together with their stickman accomplices, were everywhere in the crowds, in the underground, on railway trains […]"proscribedsometimes