IF, EVEN IF, ONLY IF, AS LONG AS, PROVIDED, SUPPOSING, UNLESS, BUT FOR, IF NECESSARY, IF SO, IN CASE etc. IF and WHEN When can replace if in zero conditionals: If you heat water to 100 degrees Celsius, it boils. When you heat water to 100 degrees Celsius, it boils. In the other types of conditionals, we cannot use when instead of if . EVEN IF Even if emphasises that something will happen, would happen or would have happened whatever the condition: Even if we leave right now , we still won't catch the train. I wouldn't go into the water even if I could swim . Even if we had booked our flight earlier , it wouldn't have been cheaper. ONLY IF Only if makes the condition more restrictive: Acetaminophen is dangerous to children only if dosage is too high. If the if -clause is first, the subject and the auxiliary in the main clause are inverted: Only if you like classical music is it worth coming tonight. SO/AS LONG AS, PROVIDING/PROVIDED