(2016-09-03, 12:49 am)RawrPk Wrote:
Rubin Wrote:wa dumps its emphatic load on what comes after it. This makes it very different from ga, which emphasizes what comes before it.
This gives a great introduction as to how wa works and how it shouldn't be used. Try and find the book at the local library and read the rest Hope this helps!
My dry reasoning for telling the difference is from simple sentences my 先生 used:
I am Tanaka.
I am Tanaka (Tanaka *points at self*, that's me!)
It's not 'new information' vs. 'old information', it's emphasized and unemphasized information. As a general rule, you're not going to emphasize the old information which is why that 'rule' sort of works sometimes. It's also why the 'topic' vs. 'subject' kind of works sometimes... the topic you're addressing sets the ground but isn't the point you're making, the stuff after the topic marker is where the point is.
The emphasis with が is not quite as certain - が is, after all, the grammatical particle for marking the subject of a verb so it may emphasize what comes before it, or it may be a fairly neutral statement (both the part before and the part after the が are simply part of a subject+verb clause, indispensable to each other and neither really 'emphasized'; this is especially likely for independent clauses embedded in a larger sentence.) It is certain, however, that the clause after the が is not emphasized over the clause before the が.
The only other case, really, is that of contrasts. (リンゴは果実ですが、ニンジンは野菜です。)
This is arguably just a special use of placing emphasis and not a different case at all; many people make that claim, certainly.
However, the 'I am Tanaka' example is the one that I usually reflect on when trying to interpret a sentence, or trying to write one although I don't do much of that.
One thing about the Tanaka example too, is that the sentences occur naturally in certain cases,
（To a person) Who are you?
私は田中です。 (emphasizes the name as conveying it is the point of the sentence)
（To a room of people） Which of you is Tanaka?
私が田中です。 (emphasizes the self, as identifying oneself out of the crowd is the point of the sentence.)
It may also be worth reflecting that in AはBです sentences, you have the following equivalence,
AはBです <-> BがAです
AがBです <-> BはAです
This kind of equivalence doesn't exist in verb-ending sentences, but copula-ending sentences are quite common so it's useful to keep in mind. Also question words can't be topics, so some sentences cannot be transformed. And of course using this transformation on 私は田中です results in a grammatical but unnatural sentence, because there are only a handful of patterns that are expected when a person introduces themselves. The other question can, however, be reasonably answered with 田中は私です.