/jp/ - Otaku Culture

[Anonymous No.]

Hello, /jp/. I finished katakana a couple of days ago, and have started learning the grammar. I'm still at particles though, as something really confuses: the が particle.

ボブは魚が好きだ。
Bob likes fish. This much I can understand, as が is referring to something that was being talked about, ボブ.
Replacing が with は would turn this into "Bob" "Fish likes" I assume. Then:

俺の妹がこんなに可愛いわけがない
Why is が used here? Isn't the topic "俺の妹"? Why not は?

I'm not getting this at all, honestly. How do you usually use it? Practice, or by rule?

Picture unrelated.

[Anonymous No.]

>>>/lang/

Fucking christ, we need a sticky for this.

[Anonymous No.]

>>6971711
... I didn't know about it. Oops.