if

CONDITION

A1used to say that something can or will happen only when something else happens or is true

• If it rains, we'll stay at home.
• You can borrow my bike if you need it.

WHETHER

A2used to ask or talk about which of two possible things is true

• She asked me if I was hungry.
• I don't know if he's coming.

WHENEVER

B1every time that something happens

• If I drink coffee late, I can't sleep.
• My dog gets excited if anyone comes to the door.