if

An uncertainty, possibility, condition, doubt etc.

Supposing that, assuming that, in the circumstances that; used to introduce a condition or choice.

“If it rains, I shall get wet.”

In the event that a statement is true (a programming statement that acts in a similar manner).

“If A, then B, else C.”

Supposing that; used with past or past perfect subjunctive indicating that the condition is closed.

“I would be unhappy if you had not talked with me yesterday.”

Supposing that; given that; supposing it is the case that.

“If that's true, we had better get moving!”

Although; used to introduce a concession.

“He was a great friend, if a little stingy at the bar.”

(sometimes proscribed) 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.”

(usually hyperbolic) Even if; even in the circumstances that.

Introducing a relevance conditional.

“I have leftover cake if you want some.”