The difference between the particles "は" and "が" depends on whether the subject or the predicate of a sentence is emphasized.
- "が" is used when you want to emphasize the subject, which means “when you want to emphasize/identify the subject out of other possibilities”.
- "は" is used when you want to emphasize the predicate, which means “when you want to emphasize the information that comes after ” は”.
- Meg : Who ate my ice cream?
誰が私のアイスを食べたの？ - Amy : I don’t know who did, but I didn’t.
分からないけど、私は食べてないよ。 - Ken : If you’re talking about the strawberry one, Leo ate it a little while ago
苺アイスのことを言っているなら、ちょっと前にレオが食べていたよ。