| > The particle "ga" and "wa" both introduce a topic Forgive me for saying this, since you seem to be a native speaker, but don't you mean that they both introduce the subject, not topic (using 'topic' as a linguistic term)? "Wa" would be the topicalising subject marker, denoting known information: Tanaka wa nihon ni itta. Tanaka went to Japan. -> As for Tanaka, he went to Japan.
Tanaka = known information (i.e. Tanaka is familiar to the listener) "Ga", while also a subject marker could denote/introduce new information: Tanaka ga nihon ni itta. Tanaka went to Japan. -> e.g. It was Tanaka who went to Japan. Tanaka = new information (e.g. the listener is did not not Tanaka was the one going to Japan.) (Note: I realise there are other constructions for my interpretation of the ga-sentence) |
Your explanation of 'ga'/'wa' is spot on as far as I can understand as a layman of native speaker with standard Japanese grammar education in Japan but no advanced linguistic degree.
I'd say that, because 'wa' emphasizes the introduced subject as the center of interest, it isn't used in the subordinate clause.
Tanaka ga nihon ni itta hi. (The day Tanaka went to Japan) ; ok - the interest is on 'hi'
Tanaka wa nihon ni itta hi. ; invalid