Help Topic/Subject confusion

I'm having trouble with some basic grammar. My grammar book is talking about making something the topic of a sentence:

1. Making Noun+structure particle the topic of a sentence

ex: Tanaka-san ga kitte o kaimashita (Tanaka-san bought stamps.)

The book then uses some cartoon example of a guy holding up a "wa" sign which is supposed to explain that to make it the topic you change ga to wa:

ex: Tanaka-san wa kitte o kaimashita (As for Tanaka-san, she bought stamps.)

My question is, what is the difference?? What's the difference between when it was a subject in the first example and when it's a topic? Can somebody give me some more examples and a more understandable explanation?

If this matters, there's also another example with a conversation:

Q: Tanaka-san wa kinoo doko e ikimashita ka.
(Tanaka-san, where did you go yesterday? <- I think that translation is wrong, I translated it as "Where did Tanaka-san go yesterday?" but what do I know...)

T: Yuubinkyoku e ikimashita. (I went to the post office.)

Q: Nani o kaimashita ka. (What did you buy?)

T: Kitte o kaimashita. (I bought stamps.)

Q: Hagaki mo kaimashita ka. (As for postcards, did you buy them too?) *They put emphasis on mo, as they're making the hagaki the topic by using mo.

T: Iie, hagaki wa kaimasen deshita. (No, postcards I didn't buy.) *Emphasis on the use of wa.

What would be the difference if I translated that last part as "Iie, hagaki o kaimasen deshita," or "Iie, hagaki ga kaimasen deshita"? Up until reading this I've been using 'o' so if I was in that situation I would have said "Iie, hagaki o kaimasen deshita." How does the use of wa change it and how do I know when to use wa?

Confused!!!!!

A Good Book that helps me.

"A Dictionary Of Japanese Particles" by Sue A. Kawashima has tons of examples and explanations. Got it at Borders. It explains things in an easy way to understand; very down to earth.

Frank

Here's are some pretty good past threads as well.

ga and o particles | Japan Forum

particles - ni, ga, o (wo) | Japan Forum

ex: Tanaka-san ga kitte o kaimashita (Tanaka-san bought stamps.)

ex: Tanaka-san wa kitte o kaimashita (As for Tanaka-san, she bought stamps.)

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That will depend what the question is or what you want to emphasize on.

First sentence's question would probably be:
dare ga kitte o kaimashitaka ?
Emphasis is on dare. ga usually emphasize what's before it.

Second sentence's question would probably be:
Tanaka san wa nani wo kaimashita ka?
wa gives listener to look forward to the detail of what comes after wa. wa is like "as for"

:
T: Yuubinkyoku e ikimashita. (I went to the post office.)

Q: Nani o kaimashita ka. (What did you buy?)

T: Kitte o kaimashita. (I bought stamps.)

Q: Hagaki mo kaimashita ka. (As for postcards, did you buy them too?) *They put emphasis on mo, as they're making the hagaki the topic by using mo.

T: Iie, hagaki wa kaimasen deshita. (No, postcards I didn't buy.) *Emphasis on the use of wa.

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As mo means "also" I think this is more suitable than anything else.

If there are more questions after this like
Q: hako mo kaimashita ka?
T: iie, hako mo kaimasen deshita.
mo is used rather than wa because previous sentence is also "did not buy" and thus no need wa to contrast the answer. It would now mean "I also did not buy a box"

as for last answer, wa is used because it's contrasting the first question.

T: I went to post office
Q: What did you buy
T: I bought some stamps
Q Did you also bought postcard
T: Well, as for postcards, I didn't buy them

So, when you mean to say the last statement above, "iie, hagaki wa kaimasen deshita" becomes the more proper word, don't you think so?

I've not seen "o" used on negative question. I could not explain it either except to say that it sounds weird. If you what to say, "iie, hagaki ga kaimasen deshita", then the question would be "nani ga kaimasen deshita ka". Emphasis is "what is it that you didn't buy?"

so in brief, wa is use for 2 purposes...
1) To throw the emphasis to what comes after wa
2) To contrast thing. it could be either on the same sentence itself or immediately before this sentence.

Another simple example

hambaagaa wo tabemashita
hambaagaa ga tabemashita

1st sentence means eat the hamburger
2nd sentence means hamburger eat something (hee hee)

Originally posted by beluga
I've not seen "o" used on negative question. I could not explain it either except to say that it sounds weird. If you what to say, "iie, hagaki ga kaimasen deshita", then the question would be "nani ga kaimasen deshita ka". Emphasis is "what is it that you didn't buy?"

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I don't think it sounds strange at all to say "What didn't you buy?" using wo, if it appears someone has overspent or bought almost everything else for instance. "Nani ga kaimasendeshita ("was there something in particular you didn't buy?") we almost never say in English.

Originally posted by beluga
That will depend what the question is or what you want to emphasize on.
As mo means "also" I think this is more suitable than anything else.

If there are more questions after this like
Q: hako mo kaimashita ka?
T: iie, hako mo kaimasen deshita.
mo is used rather than wa because previous sentence is also "did not buy" and thus no need wa to contrast the answer. It would now mean "I also did not buy a box"

Click to expand...

I think "wa" would be most natural if you had previously talked or thought about buying a box, in that case just "hako wa?" (what about the box?") is fine.