With my new-found knowledge, I'm now attempting to analyze another sentence:
"Anata wa nihongo ga hanasemasu ka?"
Since this is the beginning of a conversation, WA is obviously not marking information about a topic already identified. So let's say it's emphasizing the following word, i.e. "nihongo."
As for GA, it is marking "nihongo." I guess you could say "nihongo" is the subject of the sentence, but it's not the grammatical subject. From an English grammar perspective, the subject is "you" and the direct object is "Japanese."
So it seems to me that it might be equally valid to say:
"Anata wa nihongo o hanasemasu ka?"
... because "nihongo" seems to be the direct object. Am I right?
Lesson 3.2, Wa and Ga