If vs. Whether (Simple Guide)

Both if and whether can mean “〜かどうか”.

 Both Ok

  • I don’t know if he is coming.

  • I don’t know whether he is coming.

 In conversation, if is more common.

Use Whether (not if)

1. Before “or not”

  • I’m not sure whether he will come or not.

2. After a preposition（前置詞のあと）

  • It depends on whether we have time.

3. Formal writing (more natural)

Use If for condition（〜なら）

  • If it rains, we’ll cancel.

Quick rule:
 Condition → if
 “〜かどうか” → usually whether


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