Hi. I would like to explain how I understand the difference between が and は, and for someone to confirm, correct, or comment on it. I apologise for posting on such a cliche topic, but I thought this would be the most efficient way for me to confirm my knowledge. Also, I understand that there are other uses for each – I just want to compare cases where their uses are similar (as topic and subject markers). My understanding goes like this:
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**tl;dr:**
\- ‘Introduction by が; known info by は’.
\- が is also used to emphasise things generally.
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**Proper:**
There are two aspects in which が and は differ: 1) whether or not the thing or person in question is in both speakers’ shared context, 2) emphasis.
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*Aspect 1.*
は is used in the following contexts, regarding this aspect:
1. When the thing or person denoted by it has already been mentioned in the conversion.
2. When the thing or person denoted by it is a proper noun – a specific person, a specific place, a title. E.g., ‘Japan’.
3. When the thing or person denoted by it is closely known by both speakers. E.g., the speakers’ common friend Tanaka-san, ‘I’, ‘you’.
4. When the thing or person denoted by it is one of its kind. E.g., ‘the sun’, ‘the shougun’.
5. When the thing denoted by it is a whole variety/sort of thing (i.e., a generic name). E.g., ‘pine’.
6. When the thing denoted by it is already specified by a demonstrative. E.g., ‘this book’.
The common feature of all of these is that both speakers know exactly what/who the thing or person in question is. In the first point, this was introduced/specified earlier. In the second, third and fourth, only one of these exists, so it needs no introduction/specification. In the fifth, you are speaking of an entire class of thing, so it is unique and also does not need specification. In the sixth, you already specify it with a demonstrative, so it needs no further specification.
が is hence used in every case that you need to denote a subject in, that is not one of the above cases. が is also used when the subject is an interrogative. This is because what an interrogative is referring to is not known (as it is an interrogative), so it wouldn’t make sense to use は.
The first above case is probably the most common. Given these rules for using が and は, when talking about some thing or person (that does not fit into the other cases), you would use が to introduce it/them and then if necessary refer to it/them with は in later sentences.
E.g.: 本が椅子から落ちた。本は高かった。
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*Aspect 2.*
が is used to emphasise the subject. E.g., ‘*She* ate the apple’.
は is used to emphasise the predicate (or rather just not emphasise the subject). E.g., ‘She *ate the apple*’.
This is somewhat related to the first aspect. It makes sense to emphasise something/someone that is being introduced/specified for in the conversation for the first time. Then in subsequent sentences containing this/them, it makes sense to emphasise the predicate, because it/them would already be known, old information.
This ‘introduction by が; known info by は’ rule also applies to the other 4 cases above.
However, I think this aspect is slightly more flexible than the first. You can generally use が to emphasise/single out something in cases unrelated to this rule. For example, you can say ‘俺がやる’ to mean ‘I’ll do it \[rather than someone else\]’, without any relation to this rule.
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Edit: typo.
1 comment
Your first aspect is absolutely right, but I’d be cautious about the second one. Do you know the contrastive use of は？As in それは分からないけど、これは分かるよ。You could very well say that the は in that case is adding “emphasis” too. It’s more specific than that, but “emphasis” is kind of too fuzzy a word to be helpful, because both が and は can be seen as adding emphasis in their own ways. I’d argue that your aspect #2 is simply aspect #1. Your 俺がやる example is still aspect #1, because the 俺 is in this case new information–it answers the implied question 誰がやるの？ and *not* the question あなたは何をするの？