Whether or If?
If – implies probability / conditionWhether – indicates a choice between alternatives
“I’ll only stay if you offer me more money” involves a condition, not a choice and therefore if is correct. But, “He seemed undecided whether to go or stay” conveys two alternatives, so whether is better.
Further examples:
“You would know what was going on if you had listened.”
“Mike didn’t know whether James would arrive on Friday or Saturday.”
Note: When the sense of whether is “regardless of the possible alternatives”, include the phrase “or not”.
“Call him if you are going to arrive on Friday.”
“Call him whether or not you are going to arrive on Friday.”
Adapted from DailyWritingTips
