[dasfasf]

A interesting property of Japanese is that a sentence is also a subordinate clause. For example

Tarou wa Noriko wo toshokan de mimashita. (Tarou saw Noriko at the library.)

Tarou wa Noriko wo mimashita. (Tarou saw Noriko.)

Tarou wa Noriko wo mimashita toshokan (The library where Tarou saw Noriko)

Generally "<sentence> <noun>" means "the <noun> such that <noun> <particle> <sentence> is true for some choice of <particle>".

[shiro]

Your third example isn't valid. It needs a bit of tweak.

Tarou ga Noriko wo mita toshokan

The particle "ga" and "wa" both introduce a topic. But in a phrase to explain a noun, we use "ga" exclusively. Your main point still holds, in a sense that "Tarou ga Noriko wo mita" is a valid sentence. But to be precise, "mita" in those two sentences are different conjugated forms; it just happens that two conjugated forms are the same in the verb "miru" (to see).

[blipmusic]

> 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)

[blipmusic]

1. You can't topicalise the subject of a subordinate clause. 2. Only plain form is valid for verbs in a subordinate clause. (maybe the particle "kara" could be seen as an exception here)

[kazinator]

"anata ga kukkii wo taberu" (you eat the cookie)

"anata ga kukkii wo taberu no wo mita yo" (I saw you eat the cookie)

"Anata" is now the subject of a subordinate clause.

I think it can be topicalized (in the sense of becoming the grammatical topic, marked by ha) like this:

"Anata ha, kukkii wo taberu no wo mita yo". (As for you, I saw (you) eat the cookie.)

The subordinate clause now has an unspecified/implicit subject, and that identifies with the topic that was introduced.

I think an extraposition of "anata" (into a non-topical position) is possible like this, where subordinate clause minus its subject is now the topic:

"kukkii wo taberu no wo mita ha, anata da yo". (the one I saw eating the cookie is you)