Want to know when to use “if and when”? Check this out and find out.
dictionary.cambridge.org explained the difference between if and when by stating, “We use if to introduce a possible or unreal situation or condition. We use when to refer to the time of a future situation or condition that we are certain of.”.
When I turn 18, my parents will buy me a new car. (This is a future situation that the speaker is certain of.)
If get high grades this year, my parents will buy me a new car. (The speaker is talking about a possible condition).
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