if

Supposing that, assuming that, in the circumstances that; suppositive used to introduce a condition that may be (or prove to be) either true or false.

• I'll do it next week if I have time.
• Fetch me a cold beer if there's one in the fridge.
• If I give you the money, will you buy it for me?

A keyword that invokes conditional processing: in the event that a given condition is true, execute the given statement(s) (otherwise execute other statements).

• if A then B else C

Supposing that; used with past or past perfect subjunctive to indicate a counterfactual or hypothetical condition.

• If she hadn't told me, I wouldn't know.
• If he understood how this made me feel right now, he'd be O.K. with it too.
• If I was King of England, I'd make you my Queen.

Even if; even in the circumstances that.

• I wouldn't marry you if you were the last man on earth.
• You're finishing your chowder if you sit there all afternoon!

Considering the fact that; given that; introducing a condition that is known to be true.

• The drain's blocked — and if the drain's blocked, the water won't flow.

When; whenever; every time that.

• If you heat water to 100° C, it boils.
• If it rains, it pours.

Although; used to introduce a concession; may..but.

• He was a great friend, if a little stingy at the bar.
• She won her team's admiration, if not the award, for her performance.

While; used to introduce a contrast.

• If tea is expensive, coffee is completely unaffordable.

Whether; used to introduce a noun clause, an indirect question, that functions as the direct object of certain verbs.

• I don't know if I want to go or not.

Introducing a relevance conditional; in case.

• I have leftover cake if you want some.
• If you want to go home, I have the car keys.

An uncertainty, possibility, condition, doubt etc.

• The board can't approve this project; there are too many ifs.