One of the most difficult aspects of learning Japanese is the difference between particles は and が. It is difficult because these two particles do not have counterparts in English. And most of the time substituting one with the other will only change the subtle meaning of a sentence. The sentence will remain grammatically perfect.
For instance, both
are grammatically correct. But their meanings are subtly different.
So how different?
Before explaining the details, let’s review the functions of the two particles:
は is used to indicate the topic of a sentence. The focus of the sentence is the statement behind the particle は.
が is used to indicate the subject of a sentence. The focus is the subject before the particle.
At least this is what the textbooks say. But because the definitions of Japanese topic and subject are very unclear, e.g. the function of 私は in sentence A is like a subject in English sentence, using topic-subject to explain the difference between は and が will most of the time take you nowhere or even get you more confused.
To make things easier to understand, we will analyze things from another angle and take the situation approach. In other words, we will discuss in which situations we should use は or が.
Situation 1: Exclusive VS Non-exclusive
Sentence A simply tells listeners that “I am an American”. We cannot change it to アメリカ人は私です (American is me), because we know that I am not the only American in the world. In this case, アメリカ人 does not apply to 私 exclusively. It applies to many other people at the same time.
On the other hand, sentence B is only used in a situation where I am the only American, e.g. a group of 8 exchange students from 8 different countries sitting in a room. When the teacher asks, “誰がアメリカ人ですか。(Who is American? )”, you should say “私がアメリカ人です”, because in this situation アメリカ人 applies exclusively to 私. If you use は, you will sound strange as if your teacher ask you about apples and you tell her about oranges. “私がアメリカ人です” in this case can be changed to “アメリカ人は私です”
So when we say トムは犯人だ (犯人means offender of a crime), we imply that there may be other offenders. But if we use トムが犯人だ, then we imply that Tom is the only offender.
Situation 2: Specific Vs General
C. 鳥は飛ぶ (general)
D. 鳥が飛ぶ (specific)
Sentence C is describing a general fact that birds fly. Listeners will not have a specific bird in their mind. But sentence D is describing a scene that a specific bird or group of birds fly. So when you see a bird fly and want to tell your friend about it, you should use sentence D (actually, progressive form 飛んでいる (flying) sounds more natural). If you use sentence C, you are telling your friend a scientific fact instead of your observation.
Situation 3: Old information Vs New information
When you use sentence E, you assume that your listeners already know who is トム(Tom). Either you have mentioned it before or both you and the listeners already know him, e.g. Tom is a movie star. If your listeners do not know Tom, then you should use sentence F to introduce him. After this introduction, you can use は, e.g. トムがいい人です。彼は私の同僚です。
For this reason, question words (wh-words in English) cannot be followed by は because they are asking for new information. So after だれ, どこ or いつ, don’t think. Just useが.
Situation 4: は and が are used at the same time
G. 山田さんは妻がきれいです (Mr Yamada’s wife is beautiful)
The literal part by part translation of this sentence is: About Mr Yamada, wife is beautiful.
“aはbが…” is a very common Japanese sentence structure. ‘a’ is the topic. ‘b’ is something related to ‘a’. And the ‘…’ part is the information about ‘b’. “aがbは” is extremely rare.
Situation 5: は…は… for contrasting
H. 平仮名は読めるけど、漢字は読めない (I can read Hiragana but can’t read Kanji.)
The literal translation is ‘Hiragana, I can read, but, Kanji, I can’t read’. When making contrast between two sentences with opposite meanings, は…は… form is commonly used.
Situation 6: standard sentence structure that がmust be used
The good news is that there are some verbs/ adjectival nouns that must follow が.
- できる(can) e.g. 英語ができる (I can speak English)
It also applies to other ability verbs such as 聞こえる(can hear), 見える(can see),読める(can read), etc.
- わかる(understand) e.g. 英語がわかる (I understand English)
But be careful that although 知る (know) has similar meaning, it follows を instead of が. And 知る is usually used in the form of 知っている.
- 要る(is necessary) e.g. 時間が要る (It takes time)
In negative form, however, sometimes it follows は, e.g. お金は要らない (I don’t need money).
- 好き(like) e.g. 僕は君が好きだ (I love you).
As shown in the example, が in this case indicates the object of an action. (For you information, from僕は君が好きだ, we know that ‘I’ is a boy and ‘you’ is a girl, because 僕 is used by male only.)
- 嫌い(hate) e.g. 私はパパイヤが嫌いだ(I hate papayas).
- 上手(good at) e.g. 彼は英語が上手だ(He is good at English).
- 下手(weak in) e.g. 彼は英語が下手だ(He is weak in English).
- 欲しい(want) e.g. 水が欲しい(I want some water).
- いる・ある(there is) e.g. 犬がいる(There is a dog/ There are dogs).
Situation 7: は can combine with other particles but が cannot
はcan be put behind other particles to form combinations. とは and には in I and J simply mean と and に respectively. は does not change the meaning but indicate the topics of the sentences.
When studying the difference between は and が, we should never think out of context. The choice of は or が depends on situation instead of sentence structure. It doesn’t make any sense at all if we explain the difference between 私は日本人です and 私が日本人です without considering two different situations. And the standard topic vs subject explanation is very difficult for non-native people to understand.
Next time when you ask a native speaker whether your choice of はor が is correct. You must tell him exactly what you want to say, e.g. you want to say a bird in front of you is flying or you want to tell people that birds can fly.