topic marker (は) vs subject marker (が)
Core rule: は marks the topic (what we're talking about — already known, shared context). が marks the subject (new information, focus, or the answer to a question).
When が is required:
- Question words as subject: 誰が来た？ who came? — never は here.
- Answers to those questions: 田中さんが来ました.
- Existence sentences (ある・いる): 公園に子供がいる there's a child in the park — the child is new info.
- Subordinate clauses: 私が言ったこと the thing (that) I said — inside the clause, use が.
- Descriptive observations: 雨が降っている it's raining (reporting what you see).
When は takes over:
- Introducing / re-introducing a topic: 私は学生です (as for me,) I'm a student.
- Contrast: 肉は好きだけど、魚は嫌い I like meat, but fish I don't.
- Generic statements: 象は鼻が長い elephants have long noses — 象は is the topic, 鼻が is the subject inside the comment.
Heuristic that works 80% of the time: if the noun is new information the listener didn't know about, use が; if it's already on the table, use は. Question-word sentences are the reliable diagnostic — they force が.
Furigana is above every kanji; the pattern is already filled in.
私学生です。
I am a student. (introducing myself — topic)
誰来ましたか。
Who came? (question word takes が)
机の上に本あります。
There is a book on the desk. (existence — new info takes が)