が Particle

In Japanese, the ga が particle has several functions.

Subject Marker

The ga が particle is a subject marker, which means it marks the noun that comes before it as the subject of the sentence. The easiest way to understand this is with adjectives.

sora ga kirei da
空が綺麗だ
The sky is pretty.
- sora 空
  Sky. (the article, "the" or "a," is implicit.)
- kirei 綺麗
  Pretty. (na な adjective.)
- da だ
  Is.
  Are. (plurality is implicit.)
sora ga kirei datta
空が綺麗だった
The sky was pretty.
- datta だった
  Was.
neko ga kawaii
猫が可愛い
Cats are cute.
- neko ga 猫が
  Cats.
- kawaii 可愛い
  Is cute. (i い adjective.)
neko ga kawaikatta
猫が可愛かった
The cats were cute.
- kawaikatta 可愛かった
  Was cute.

One mistake people make is thinking that ga が means "is" just because it's in the middle of the two words just like in English.

XがY
~~X is Y.~~ (wrong, but depending on the phrase it could be right.)

That's not what it means. In Japanese, the verb, or copula, doesn't come in the middle of the sentence between words like in English. It normally comes at the end of the sentence.

XがYだ
X is Y. (da だ is a copula, it translates to "is," a copulative verb.)
Xが可愛い
X is cute. (with i い adjectives, the i い suffix is the copula.)

Because it's at the end, sometimes it's called Subject-Object-Verb, or SOV, as opposed to English's Subject-Verb-Object, or SVO.

Active Agent Marker

The subject marker ga が marks the agent in the active voice, which is the one doing the action.

watashi ga kiita
私が聞いた
I heard.
- kiku 聞く
  To hear.
- Here, "I" is the agent doing the action "to hear."

In this case, the wo を particle generally marks the direct object.

watashi ga sore wo kiita
私がそれを聞いた
I heard that.

The ni に particle can mark the indirect object.

watashi ga kare ni kiita
私が彼に聞いた
I heard from him.
watashi ga sore wo kare ni kiita
私がそれを彼に聞いた
I heard that from him.

Passive Patient Marker

The subject marker ga が marks the patient in the passive voice, which is the one receiving the action.

In Japanese, the passive voice is expressed by conjugating the verb to its passive form.

korosu
殺す
To kill. (active voice.)
korosareru
殺される
To be killed. (passive voice.)
kare ga koroshita
彼が殺した
He killed. (active voice.)
kore ga korosareta
彼が殺された
He was killed. (passive voice.)

To mark the agent in the passive, the ni に particle is used instead.

kare ga ninja ni korosareta
彼が忍者に殺された
He was killed by ninjas. (i.e. ninjas killed him.)

Note how the patient of the passive (marked by ga が) is basically the same thing as the object of the active voice (marked by wo を).

neko ga nezumi wo kutta
猫がネズミを食った
The cat ate the rat.
nezumi ga neko ni kuwareta
ネズミが猫に食われた
The rat was eaten by the cat.

Patient vs. Direct Object

Grammatically, the patient and the direct object aren't the same thing. In practice, they're often pretty much the same thing. But there are cases where their difference shows.

Such case is when you have a passive verb, thus a sentence in passive voice in Japanese, but you have both a subject marker and a direct object marker.

kare ga kazoku wo korosareta
彼が家族を殺された
(???)

Naturally, you can't have two direct objects for a single verb. That's illegal.

You can have a single noun phrase that represents multiple things, like "two cats," but you can't, syntactically, have two different nouns marked as direct object.

So what's happening here? Simply put, you have a distinct patient and direct object.

The patient is to whom the action is applied.

The direct object is an argument for the verb.

Thus:

kazoku wo korosu
家族を殺す
To kill a family. (active voice.)

Is the same thing as:

kazoku wo korosareru
家族を殺される
To kill a family. (passive voice.)

Since it's the same type of argument (direct object) for the same verb. The only difference is that the voice has changed. When you add a subject to the equation, you get:

kare ga kazoku wo koroshita
彼が家族を殺した
He killed the family.
He killed [his] family.
- He is the agent, so he is doing the things, he is the one who knocks.
kare ga kazoku wo korosareta
彼が家族を殺される
He (patient) (plus) killed the family.
His family was killed.
- He is the patient, to whom things are being done.
- This whole "family killing" thing was done to him.
- Thus, we can assume "his" family was killed, even though we do not have a particle that indicates possessiveness in the sentence.

Assuming it was "his" family that was killed, the phrase above could be paraphrased as:

kare no kazoku ga korosareta
彼の家族が殺された
His family (patient) killed.
His family was killed.
The "killing" thing was done to "his family."

Disparity with English Subjects

The ga が particle consistently marks the subject of a sentence for a verb in Japanese. However, that doesn't mean the marked noun will always translate to English as the subject.

That is, the grammar is consistent within the Japanese language. There, the subject is always the subject. But once you take it out of the Japanese language, that consistency disappears. For reference, I'll list some ways the Japanese subject can become something else in English.

The most obvious case is when you have a verb in English that takes the pronoun "it." That's because Japanese doesn't have the pronoun "it." So when "it" is the subject in English, it certainly isn't the subject in Japanese, because it doesn't exist there.

okane ga kakaru
お金がかかる
It costs money.

In Japanese, okane, "money," is subject, but in English that's the object, and "it" is the subject. Why this happens?

Transitivity

Transitivity is the ability of a verb to take an object, or not. A transitive verb can have objects. An intransitive verb can not.

The verb "to kill" is transitive in English.

The ninja killed the samurai.
- The ninja - subject.
- To kill - verb.
- The samurai - object.

Meanwhile, the verb "to die" is transitive. The samurai dies. It's not: "the ninja dies the samurai."

The problem arises when you have an intransitive verb in Japanese, but a transitive translation in English. In this case, "to cost" is transitive. Something costs something. But kakaru is intransitive. Something just kakaru's, and it stops there.

If we were to translate literally, we'd get this:

okane ga kakaru
お金がかかる
Money costs.

This sounds like a noun in English. Like we're talking about the costs that are in money. The monetary costs. The money costs. Another example:

jikan ga kakaru
時間がかかる
Time costs.
It costs time.
It takes time.
dore dake jikan ga kakaru
どれだけ時間がかかる
How much "time costs."
How much time it takes.
How long it takes.

As you can see, the subject in Japanese ends up becoming the object in English in such cases.

Although in the examples above we have "it" as the subject in English, not all verbs end up like that. The ones that don't also happen to be weirdest ones.

For example, wakaru 分かる means something "is understood." The subject is the thing understood, not who understands the thing, like it would be in English.

sore ga wakaru
それが分かる
That is understood.
[Someone] understands that.
[I] understand that.

Another example is the verb mieru 見える. When it's used, it means something "is seen" by someone. This one often translates to someone "can see" something.

yuurei ga mieru
幽霊が見える
Ghosts are seen.
Ghosts are visible.
[Someone] can see ghosts.
[I] can see ghosts.

Note that many verbs in Japanese have a transitive and an intransitive counterpart. The easiest one to understand is "to rise," since English also has "to raise," which is transitive.

te ga agatta
手が上がった
The hand rose. (on its own?!)
te wo ageta
手を上げた
[He] raised [his] hand.

Noun Becoming a Verb in English

In some cases, a noun in Japanese can become a verb in English. This is simply a matter of saying things differently.

One notable case where this happens is this one:

ame 雨
Rain. (noun.)
furu 降る
To fall [from the sky].
To rain. (verb.)
ame ga furu
雨が降る
"The rain rains."
It rains.

Clearly nobody would say the "rain rains" in English, that sounds silly. You say "it rains" or "it's raining," even though, in fact, it's the rain that's indeed raining. Likewise:

yuki ga furu
雪が降る
"The snow rains."
It snows.

Note that this doesn't happen only with ga が. It can happen, for example, with wo を, too.

kotae wo machigaeru
答えを間違える
"To wrong the answer."
To answer it wrong.

Another notable case happens with the nouns suki 好き and kirai 嫌い. These are particularly confusing due to their origin. They come from the verbs suku 好く, "to like," and kirau 嫌う, "to hate." But the noun versions are generally preferred.

To understand how they're used, let's first familiarize ourselves with how conjugating a verb into a noun works.

kaku 書く
To write.
kaki 書き
Writing.
Written.
kaki-kata 書き方
Way of writing. The way something is written, or the way someone writes something.
kaki-nokosu 書き残す
To leave written.

Therefore:

suku 好く
To like.
suki 好き
Liking.
Liked.

The way they're used:

neko ga suki
猫が好き
~~"Cats are liking."~~ (this makes no sense.)
"Cats are liked." (this makes more sense.)

What the phrase above normally translates to is: "[someone] likes cats." Usually, we assume this someone is me. Therefore, "I like cats."

So the verb "to like" in Japanese became the noun "liked" in Japanese which translates to the verb "to like" in English. It's exactly as confusing as you think.

inu ga kirai
犬が嫌い
"Dogs are disliked."
[Someone] dislikes dogs.
[I] dislike dogs.

Existence and Possession

In Japanese, the verbs aru ある and iru いる can denote either the existence or possession of inanimate and animate objects respectively. This can translate to English in various ways.

They can translate to "there is" or "there are."

mizu ga aru
水がある
Water exists.
There is water.

They can translate to "is at [somewhere]" if a place is indicated, or "is [here]" when implicit.

neko ga asoko ni iru
猫があそこにいる
The cat is there.
neko ga iru
猫がいる
There's a cat [here].
There are cats [here].
ore ga iru
俺がいる
I'm [here].
- Not to be confused with:
- Yahari Ore no Seishun Rabukome wa Machigatteiru.
  やはり俺の青春ラブコメはまちがっている。
  As I thought, My Youth's Love-Comedy is Wrong.

Depending on context, it can mean "to have."

okane ga aru
お金がある
To have money.
[I] have money.
kareshi ga iru
彼氏がいる
To have a boyfriend.
[I] have a boyfriend.

The negative counterpart of the verb iru いる is its negative conjugation, inai いない. However, for the verb aru ある, it's the adjective nai 無い, "nonexistent."

okane ga nai
お金がない
"Money is nonexistent."
Money doesn't exist.
There isn't money.
To not have money.
[I] don't have money.
kareshi ga inai
彼氏がいない
A boyfriend doesn't exist.
A boyfriend isn't [here].
There isn't a boyfriend.
To not have a boyfriend.
[I] don't have a boyfriend.

Topic Marker Usage

You may have noticed that the disparities above raise a question, a problem, regarding how subjects work in Japanese.

The phrase "it costs money" translates to okane ga kakaru. In which case okane is the subject in Japanese, even though it's the object in English.

Then, the phrase "the surgery costs money," translates to what? Because, in English, "the surgery" is the subject. But "money" becomes the subject in Japanese. So do you end up with two subjects?

*shujutsu ga okane ga kakaru
~~手術がお金がかかる~~
~~The surgery costs money.~~ (wrong.)

In such cases, you use the wa は particle, which is the topic marker. Note that it's spelled with the hiragana that's normally read ha は, but when it's the particle it's read wa わ. There are various ways to translate it to English:

shujutsu wa okane ga kakaru
手術はお金がかかる
The surgery, money costs.
About the surgery: it costs money.
As for the surgery, it costs money.
The surgery costs money.

Similarly, to express who likes or hates something, you use the wa は particle:

kanojo wa neko ga suki
彼女は猫が好き
About her: cats are liked.
She likes cats.

Another example:

atama ga ii
頭がいい
"Head is good."
[Someone] is smart.
kare wa atama ga ii
彼は頭がいい
About him: head is good.
He's smart.

Note that wa は isn't the only particle that can function like this. The mo も particle does the same thing, but it's inclusive, translating to "too."

watashi mo neko ga suki
私も猫が好き
Including me: cats are liked.
I, too, like cats.

These can be combined with ni に to form the compound particles niwa には and nimo にも.

yume ga aru
夢がある
A dream exists.
There's a dream.
To have a dream.
kono Joruno Jobaana niwa yume ga aru
このジョルノジョバーナには夢がある
For this Giorno Giovanna: there is a dream.
This Giorno Giovanna has a dream.
- See kono ore da この俺だ for details.

Replaced by wa は

In English, the subject, which we determine by word position, and the topic, which is what we're talking about, are generally the same thing. In Japanese, the opposite happens: the topic, which is marked by wa は, and the subject, which is an argument for the verb, are often the same thing.

In a simple sentence with one main clause, when both topic and subject are the same, the wa は particle is normally used instead of ga が.

kare wa shinda
彼は死んだ
As for him, died. (literally.)
He died. (interpretation.)
sore wa kirei da
空は綺麗だ
As for the sky, pretty is.
The sky is pretty.
neko wa kawaii
猫はかわいい
As for cats, cute-is.
Cats are cute.

In the example above, the topic isn't literally the subject, and there isn't a subject declared in syntax, however, all verbs with at least one argument must have a subject.

Therefore, the subject for the copulative verb "are" in English, for example, and the copulative adjective kawaii in Japanese, must be somewhere in the discourse, otherwise it would be nonsense.

We can infer that the topic is the subject through interpretation rather than literally. That is, we interpret the literal words, and figure out what is supposed to be the subject from context. So neko is assumed to be the subject for kawaii even if it's not literally marked so.

{neko ga kawaii} no de watashi wa suki
猫がかわいいので私は好き
Cats are cute, thus, as for me, liked.
Because cats are cute, I like [them].

Above, we have the same phrase from earlier, but it's no longer in the main clause, it's in a subordinate clause of a complex sentence, specifically, a relative clause, which qualifies the nominalizer no の.

In Japanese, you can only have one topic per clause and it must be in a main clause. Every other time you'll use ga が.

Replaced by mo も

The wa は particle can always be replaced by the mo も particle, which is inclusive, translating to "too." Therefore, the ga が particle, which can be replaced by wa は, can also be replaced by mo も.

neko mo kawaii
猫も可愛い
Cats, too, cute. (besides other animals.)
kare mo shinda
彼も死んだ
He, too, died. (besides other people.)
manga mo yomu
漫画も読む
Manga, too, [I] read. (besides other books.)
watashi mo manga wo yomu
私も漫画を読む
I, too, read manga. (just like other people.)

Replacing wo を

The ga が particle marks the subject and the wo を particle marks the object, but sometimes it's not so simple, and ga が can replace wo を.

With Auxiliaries

When the verb of the sentence has an auxiliary verb or auxiliary adjective attached to it, its transitivity becomes ambiguous.

A good example of this is the auxiliary adjective tai たい, which translates to "want to [do something]" in English.

yomu 読む
To read.
yomitai 読みたい
Want to read.

As you'd expect, yomu is transitive: you read something. And something is marked by wo を.

manga wo yomu
漫画を読む
To read manga.

On the other hand, tai たい is syntactically an i い adjective. And with adjectives you only mark the subject:

manga ga tanoshii
漫画が楽しい
Manga is fun.

So when you combine transitive verb with the intransitive auxiliary adjective, you get two possibilities:

{manga wo yomi}-tai
漫画を読み　たい
"To read manga" is want.
manga ga {yomitai}
漫画が　読みたい
Manga is "want-to-read."

In this case, the correct one is manga ga yomitai. After all, you attach tai to verbs, not to noun phrases like "manga ga yomi." So the verb alone becomes yomitai, which is an adjective, which needs the ga particle.

However, because this change in part-of-speech and transitivity can be a bit tricky to understand, or even to remember mid-sentence, some people do use wo を with tai たい. ^{(がしたい～とをしたいの違い - detail.chiebukuro.yahoo.co.jp, accessed 2019-05-17)}

Similarly:

manga ga yomiyasui
漫画が読みやすい
Manga is easy-to-read.
ranobe ga yominikui
ラノベが読み難い
Light-novels are hard-to-read.

The form of the yomu verb above, yomi, is called the noun form (because it's a noun), a.k.a. the masu stem (because yomi-masu), a.k.a. conjunctive form, a.k.a. ren'youkei 連用形 form.

Not all adjectives you attach to this form are auxiliary adjectives. Some are, confusingly, adjectives which are suffixes but not auxiliaries, like the sou そう suffix.

The difference in this case is that the transitivity remains the same, so you don't replace wo を by ga が.

sore wo yaru
それをやる
To do that.
sore wo yari-sou da
それをやりそうだ
Doing that looks like [something he would do.]
sore wo yari-sou na hito
それをやりそうな人
A person [that] looks like [they] would do that.

With auxiliary verbs, it would work the same way: the transitivity of the main verb changes if an intransitive auxiliary verb is attached to the noun form of the main verb.

However, such "intransitive" auxiliary verbs attached this way don't exist. They're all transitive. So replacing wo を by ga が doesn't happen.

manga wo kiru
漫画を切る
To cut a manga.
manga wo yomi-kiru
漫画を読み切る
To finish reading a manga.

On the other hand, there's another way to attach an auxiliary: to its te-form.

kitte
切って
To cut. (te-form.)
yonde
読んで
To read. (te-form.)
yomitakute
読みたくて
Want to read. (te-form.)

In this case, wo を is never replaced with ga が.

This happens because the verb has already verb'd its verb-ness when it's in the te-form. Its clause is done. Complete. Sealed tight. You can't affect it anymore.

The te て (or de で) at the end simply delivers one verb's finished clause to the next one in the phrase. For example:

manga wo yonde → iru
漫画を読んでいる
Being "to read manga." (literally.)
To be reading manga.
- iru いる
  To be. (intransitive verb, also an auxiliary verb.)
manga wo yonde → mita
漫画を読んでみた
[I] tried "to read manga."
- miru 見る
  To see. (transitive verb.)
  To try. (auxiliary verb.)

The same thing happens to auxiliary adjectives attached to the te-form: attaching them doesn't affect the verb's clause. For example, this happen when hoshi 欲しい, "wanted," is auxiliary:

manga wo yonde → hoshii
漫画を読んでほしい
"To read manga" is wanted.
[I] want [you] "to read manga."

Note that auxiliary adjectives such as tai たい have te-forms too. The grammar is consistent: being in the te-form doesn't change anything. But, in this case, you'll have had to change wo を to ga が anyway already because of the tai, regardless of te-form. ^{(I just want to say this is the first time in my life I've used "will have had to" in a sentence.)}

manga ga yomitai
漫画が読みたい
Want to read manga.
manga ga yomitakute shini-sou
漫画が読みたくて死にそう
[I] want to read manga [so much that] [it] looks like [I'm going] to die.

The wo を particle is never replaced by ga が when you have the nai ない suffix, even though that suffix is treated like an adjective.

manga wo yomanai
漫画を読まない
Does not read manga.

In The Potential Form

Another case is that ga が can replace wo を when the verb is in the potential form.

manga ga yomeru
漫画が読める
"Manga is able-to-read."
Manga can be read.
[Someone] can read manga.
[I] can read manga.

This happens because the potential form expresses a quality about the subject: other things can't be read, but manga can, so manga is "able-to-read," for the lack of a better word.

This works just like the verbs wakaru 分かる, "something is understood," and mieru 見える, "something is seen." Because we're talking about how something is, the verb is just like an adjective, and takes a subject, not an object.

Consistent with those other cases, in this case the wa は particle marks to whom manga is "able-to-read," in other words, who can read manga.

watashi wa manga ga yomeru
私は漫画が読める
As for me, manga is able-to-read.
I can read manga.

Note that, in this case, too, sometimes wo を is used regardless.

manga wo yomeru
漫画を読める
[I] can read manga.
watashi ga manga wo yomeru
私が漫画を読める
I can read manga.

Replaced by no の in Relative Clauses

In relative clauses, the ga が subject marker can be replaced by no の sometimes.

te ga ugoku
手が動く
The hand moves.
te ga ugoku ningyou
手が動く人形
A doll [whose] hands move.
- In English, the relative pronoun "whose" introduces the relative clause "hands move" that qualifies the noun "doll."
te no ugoku ningyou
手の動く人形
(same meaning as above.)

This, of course, applies to every case ga が marks the subject, like when it's the passive patient instead:

nezumi ga kuwareta shunkan
ネズミが食われた瞬間
The moment [when] the rat was eaten.
nezumi no kuwareta shunkan
ネズミの食われた瞬間
(same meaning.)

It can happen even to the weird ones that don't translate well to English. In fact, most of the time it will be weird ones that don't translate well to English.

yuurei ga mieru hito
幽霊が見える人
A person [that] can see ghosts.
yuurei no mieru hito
幽霊の見える人
(same meaning.)

tema ga kakaru
手間のかかる
Labor costs.
It costs labor.
It takes labor.
It takes work.
tema ga kakaru gaki
手間がかかるガキ
A brat [that] takes work. (causes a lot of trouble!)
tema no kakaru gaki
手間のかかるガキ
(same meaning.)

kareshi ga iru joshi
彼氏がいる女子
A girl [that] has a boyfriend.
kareshi no iru joshi
彼氏のいる女子
(same meaning.)

atama ga ii oneesan
頭がいいお姉さん
A girl [whose] head is good.
A girl [that] is smart.
- oneesan お姉さん
  Older sister.
  A girl. Teenager to young adult.
atama no ii oneesan
頭のいいお姉さん
(same meaning.)

te ga kirei da
手が綺麗だ
Hands are pretty.
te ga kirei na josei
手が綺麗な女性
Women [whose] hands are pretty.
- See na な attributive copula.
te no kirei na josei
手の綺麗な女性
(same meaning.)

Focus Marker

The ga が particle can mark a noun as having the focus in a simple sentence. Basically, the focus is the part of a sentence that the speaker says which the speaker believes the listener doesn't know.

This concept contrasts with topic: a topic is something the listener knows about, and the speaker is talking about, forming a topic-comment structure.

Since the topic isn't the focus, the comment must be the focus, or at least part of it must be the focus.

The ga が particle can mark the focus in two distinct ways.

By making the rest of the sentence the topic, inverting the topic-comment structure into comment-topic, thereby making the first part of the sentence the focus rather than the last.
By making the whole sentence the focus, creating a topic-less sentence-focus.

These two functions are denominated exhaustive listing ga が and neutral description ga が respectively. ^{(Kuroda, Kuno 久野, cited in Shigeura 杉浦, 2018)}

Exhaustive Listing

The exhaustive listing function of the ga が particle generally means the marked noun is exclusive somehow, as it's associated with a very narrow topic, and usually the answer to a question.

This needs some elaboration. Observe the phrase below:

banana wo tabeta no wa watashi da
バナナを食べたのは私だ
The one that ate the banana is me.
- Not other people.

Above, "the one that ate the banana" is our topic. That implies we already know "some-one ate the banana."

By contrast, "me" is not part of the topic. It's part of the comment. It's also our focus. We've only said "the one that ate the banana is me," because, before we said it, people didn't know who is "the one that ate the banana." They only knew someone ate it.

The focus is the new information, that normally answers a question.

Since ga が can mark the focus of the sentence, we can shuffle the phrase above into the following:

watashi ga banana wo tabeta
私がバナナを食べた
I ate the banana.
- Not other people.

This phrase and the previous one have the same focus. And the same topic too.

After all, if focus is the information we don't know yet, and topic is the information we already know, that means if the only new information is "I," then that "[someone] ate the banana" is old information.

Once again, the topic isn't literally marked as the subject, but it can be interpreted as being the subject

One way this function is normally used it to answer questions. For example:

dare ga banana wo tabeta?
誰がバナナを食べた？
Who ate the banana?

Above, we've marked "who" as being the focus. I mean, of course. We know "someone ate the banana." We don't know "who" ate the banana. We can't mark as the topic something we literally don't know about.

*dare wa banana wo tabeta.
~~誰はバナナを食べた~~
(wrong.)
- This means:
- I know that the one that ate the banana was who.
- Since "who" isn't a person, or thing, or anything at all, it can't have done anything.
- The word "who" is an interrogative pronoun, it's just a word used instead of the word you want to use because you don't know what word would that be.
kare ga banana wo tabeta!
彼がバナナを食べた！
He ate the banana!
- "He" is the word we wanted.

A few other examples:

nani ga shitai?
何がしたい？
What is want-to-do?
What do you want to do?
- I presuppose you want to do something, but I don't know what.
doko ga itai?
どこが痛い？
Where is painful?
Where hurts?
- I presuppose somewhere hurts, but I don't know where.
itsu ga ii?
いつがいい？
When is good?
- I presuppose sometime must be good for us to schedule an appointment, but I don't know when.

This same exclusive listing ga が can also be used without the question-answer format. For example:

manga yori anime ga omoshiroi
漫画よりアニメが面白い
Rather than the manga, the anime is funny.
- Here, the presupposition is either that both are funny, or that one is funnier than the other, but we're asserting things straight: the anime is funnier than the manga.
konosuba no hou ga omoshiroi
このすばの方が面白い
The way of the konosuba is funny.
The side of konosuba is funny.
Konosuba is the funny one of the two.
- Here, only konosuba was uttered, but it's being compared to another series that wasn't uttered in this sentence, but that would be present in the context somewhere.

Cancelling Implicatures

The exhaustiveness expressed by the ga が particle is merely implied. The ga が doesn't explicitly say that "other are not." It just implies that "others they are not." ^{(Shibatani, cited in Heycock, 1994)}

This means that you can contradict this implication without sounding like you've said two contradictory things like some sort of madman.

dare ga kashikoi?
誰が賢い？
Who is clever?
watashi ga kashikoi
私が賢い
I am clever.
- Implicature: other people are not clever.

Above, although we haven't said so, it's implied that other people as clever as "me." After all, if I knew Tanaka was also clever, I could have said so: "me and Tanaka are clever."

By not saying Tanaka is also clever, I'm implying that I know he's not, or I don't know that he is. Otherwise, why would I be omitting such valuable and relevant information?

The Maxim of Quantity. ^{(Grice, 1975)}
1. Make your contribution as informative as required.
2. Do not make your contribution more informative than required.

However, the fact that I haven't literally said that "Tanaka is not clever" doesn't change. So I can cancel that implicature by adding contradictory information afterwards:

sore-kara, Tanaka mo kashikoi
それから、田中も賢い
Furthermore, Tanaka, too, is clever.
- Which means: other people are also clever.

Naturally, not all implicatures all cancellable. For example, imagine there was a match, a fight, between Tanaka and I. After it ends:

dare ga katta?
誰が勝った？
Who won?
Tanaka ga katta
田中が勝った
Tanaka won.
- Entailment: I lost.

There can only be one winner, so Tanaka winning naturally means that "I lost." You can't say "I lost" is false while "Tanaka won" is true.

If I said "Tanaka won, but I didn't lose," it sounds like I'm a liar and a sore loser, or that I'm trying to turn the final episode of a tournament arc into a melodrama about character development or something.

Neutral Description

Another function of the ga が particle is to imply a neutral description.

Basically, given that focus is new, and topic is old, you'd think that the description given by the focus is better than the already-known information called the topic.

When we don't have a topic in a sentence, that means the entire thing is new. So one part of the sentence isn't superior to the other as far as information new-ness is concerned. The whole description is neutral.

For example, imagine you're playing an RPG and you're journeying around about to save princesses, defeat kings, and stuff, when, suddenly:

monsutaa ga arawareta!
モンスターが現れた！
A monster appeared!

The sentence above has sentence-wide focus. We didn't know about any monsters, and didn't know something had appeared, therefore, both the fact that a monster exists and the fact it appeared are equally new to us.

Similarly, suppose you're into a desperate situation being attacked by villains, everything seems hopeless and your heart fills with despair, then, all of sudden, a hero breaks through a wall to save you, yelling from the bottom of his lungs:

MOU DAIJOUBU!!
NAZE TTE? WATASHI GA KITA!!!
もう大丈夫！！なぜって？私が来た！！！
IT'S ALRIGHT NOW!!
"WHY" YOU SAY?
I AM HERE!!!

Above, we knew neither of the hero, who wasn't part of the discourse because he literally just arrived, nor the fact that he just arrived, again, because he just arrived. So the entire sentence has focus.

This function is often used with exclamations containing a verb in te-iru form. For example:

ame ga futte-iru
雨が降っている
Rain is raining.
It's raining.
yuki ga futte-iru
雪が降っている
Snow is raining.
It's snowing.
sakura ga saite-iru
桜が咲いている
The cherry blossoms are blooming.

However, this happens simply because both subject and verb are the foci of the sentence. You don't normally talk about rain before it starts raining. It just comes out of nowhere. However, if you were already talking about it before:

sakura no ki wo mi-tsuketa!
桜の木を見つけた！
[I] found a cherry blossom tree!
sakura wa saite-iru!
桜は咲いている！
The cherry blossoms are blooming!

The interlocutors already know of the cherry blossoms' existence in the discourse as it was previously mentioned. So we make it the topic, with wa は, rather than the focus.

In stories, novels, if a character is introduced as doing something, they'll be introduced with ga が, since we don't know of their existence, and will be subsequently marked by wa は.

Similarly, in news stories in the format of "person X did thing Y," the first time the event is spoken about, generally in the headline and first paragraph, the person will be marked with ga が, and subsequently marked with wa は as we already know who is doing what.

Role Distinction

The functions of the ga が particle are grammatically distinct from each other in a few important ways.

Two Subjects, One Sentence

First off, as a general rule, you can't have two nouns with the same role in a single clause. That is, you can't have two nouns marked as subject.

*Tanaka ga Tarou ga nigete-iru
~~田中が太郎が逃げている~~
(nope.)

In the phrase above, we have the verb "to be escaping," nigete-iru, and we're trying to mark two people as the subject, so it would be something like "Tanaka (subject) plus Tarou (also subject) are escaping."

It doesn't work like that.

In cases like this, you have a single subject in the grammar syntax, but that's multi-word phrase instead of single word. This phrase describes the entire grammatical subject. Observe:

Tanaka to Tarou
田中と太郎
Tanaka and Tarou. (a noun phrase.)
Tanaka to Tarou ga nigeteiru
田中と太郎が逃げている
Tanaka and Tarou are escaping.

Above, the to と particle means "together." Two things are together in a noun phrase. It can even be used as a role in the clause, like this:

Tanaka ga Tarou to asonde-iru
田中が太郎と遊んでいる
Tanaka together with Tarou is playing.
Tanaka and Tarou are playing together.

However, sometimes you'll find a simple sentence with just a single clause that contains two ga が particles.

kanojo ga neko ga suki da
彼女が猫が好きだ
She likes cats.

In this case, we do not have two subjects. We have two, distinct functions of ga が. The first one is marking the focus, and the second one is marking the subject. It means the same thing as:

{neko suki na} no wa kanojo da
猫が好きなのは彼女だ
The one [that] {likes cats} is her.
- It's not anyone else.
- This is exhaustive listing.

Two Clauses, Two Subjects

You can have two subjects in one sentence, if one of them is inside a second clause instead. Because then you'd have two clauses, so you can have two subjects. For example:

watashi wa
{kanojo ga tsukutta} ryouri ga
suki da
私は彼女が作った料理が好きだ
As for me, the meal [that] {she made} liked is.
I like the meal [that] {she made}.
- Here, ryouri is the superordinate subject.
- And kanojo is the subordinate subject.

Subordinated Clauses

As we've seen before, in Japanese, the topic marker wa は can only be used to mark the topic (thus subject) in the main clause. In subordinate clauses, you normally use ga が instead.

Consequently, marking a noun with ga が in a subordinate clause doesn't necessarily express any special focus. ^{(Heycock, 1994)}

A simple example:

ou ga shinda!
王が死んだ！
The king died!
- Oh no! What a tragedy!
{ou ga shinda} ato, sensou ga owatta
王が死んだ後、戦争が終わった
After {the king died}, the war ended.
- Oh yes! What a relief!

Above, the noun ato, "after," is being qualified by the relative clause ou ga shinda.

In spite of the relative clause containing a ga particle, it doesn't express focus, that is, it's assumed we already knew that "the king died," so it isn't news to us, the news is that, after that, "the war ended," which is the focus in a main clause.

Furthermore, note the functions of the ga が particle in the literature are never simply "marks the subject." It's only two: exhaustive listing and neutral description.

Above, both clauses feature the "neutral description" function. The main clause is "neutral" because everything is equally the focus. The subordinate clause is "neutral" because nothing is the focus, also equally.

Since ga が is the default in subordinate clauses, use a wa は instead has a nuance: the contrastive topic. Which has its own kind of implicature.

{ou wa shinda} ato, sensou ga owatta
王は死んだ後、戦争が終わった
After {the king died}, the war ended.
- Implicature: in contrast to when other people died.
  - When the prince died, it didn't end.
  - When the queen died, it didn't end.
  - When the king, it ended.

Stage-Level Predicates

There's a difference about when each of the focus-marking functions of ga が can be used. That is, they can't both always be used. Sometimes it can be only one of them.

The neutral listing function (sentence-focus) can only be used with stage-level predicates. If you have an individual-level or kind-level predicate, it will be interpreted as exhaustive listing instead. ^{(Suzuki 鈴木, 2014)}

Note that, in traditional grammar, which you may have learned in school ~~if you paid attention to the classes~~, a "predicate" is the part of a clause that's not the subject. However, the explanation above is based on the Carlson classes of predicates, where a "predicate" includes the subject.

Since this is a bit complicated, let's elaborate what these Carlson classes are.

neko wa doubutsu da
猫は動物だ
Cats are animals.
- All of them. The whole kind.
kare wa nihonjin da
彼は日本人だ
He's Japanese.
- Him, as an individual.
Tanaka wa nigete-iru
田中は逃げている
Tanaka is escaping.
Tanaka is running away.
- For now, at this temporal stage.
- But he won't run away forever.

Above we have three sentences talking about things at different predicate levels. Since these are all simple sentences where topic and subject are the same thing, the topic marked wa は is used instead of ga が.

If we used ga が we would have either the neutral description or the exhaustive listing function. However, the neutral description can only be used in the last one.

neko ga doubutsu da
猫が動物だ
Cats are animals.
- Bananas are not animals.
kare ga nihonjin da
彼が日本人だ
He is Japanese.
- I am not Japanese.
Tanaka ga nigete-iru
田中が逃げている
Tanaka is running away.
- I am not running away. (or...)
- TANAKA IS RUNNING AWAY!!!
- OH MY GOD!!!
- WHAT Y'ALL DOING???
- GO AFTER HIM!!!

Above, the words in bold are the foci. Observe how kind-level and individual-level predicates have only one focus word, but stage-level predicates can also be interpreted as having sentence-focus, which is the difference between exhaustive listing and neutral description.

Accent

In such ambiguous situations, how the particle is pronounced in spoken language helps identify its function. ^{(Kuno, cited in Heycock, 1994, and in Van, 2005)}

ga が with accent: exhaustive listing.
ga が without accent: neutral description.

Conjunction

But, However

The ga が particle can also function as a conjunction, translating to "but," "however," and other words like that.

chiisai ga tsuyoi
小さいが強い
Small but strong.
Small, however, strong.
Although small, strong.
Despite being small, [it] is strong.

The conjunction function of the ga が particle is completely separate from its subject-marking function. I repeat: they're totally different things.

In fact, you can have both kinds of ga が in a same phrase. For example:

hon ga yomitai ga jikan ga nai
本が読みたいが時間がない
To read books is want, but time is nonexistent.
[I] want to read books, but [I] don't have time.

Comma Placement

Japanese uses commas to separate dependent clauses just like English.

Unlike English, however, whose conjunctions come before the dependent clause, Japanese conjunctions come after the clause that's being depended on.

In consequence, the English comma comes before the "but," but the Japanese comma comes after the ga が.

hon ga yomitai ga, jikan ga nai
本が読みたいが、時間がない
[I] want to read books, but [I] don't have time.

Fact plus Question

The conjunction ga が can also used to ask questions. It joins a fact, normally what happened or what you intend to do, plus what you want to know about it. For example:

ninja ni naritai no desu!
忍者になりたいのです！
[I] want to become a ninja!
- -i no desu ～いのです
  Copula after nominalizer after adjective.
  Adjective turned into a noun for the copula.
  Often used when explaining things.
ninja ni naritai no desu ga, dou sureba ii desu ka?
忍者になりたいですが、どうすればいいですか？
[I] want to become a ninja but, "how do good is"?
[I] want to become a ninja but, how should [I] do?
- What do I have to do?

Sentence-Ending Particle

Like basically every other particle, the ga が particle can end a sentence in diverse situations, for diverse reasons, with each and every one of its functions.

Due to Repositioning

Although usually the subject, direct object, and indirect object follow a certain order in Japanese, the grammar doesn't have strict requirements regarding which one comes before which.

This means that, as long as the proper marker comes after the noun, it can be literally anywhere in the phrase, including at the end of it.

neko ga nezumi wo kutta
猫がネズミを食った
The cat ate the rat.
nezumi wo kutta, neko ga
ネズミを食った、猫が
Ate the rat, did the cat.

Due to Implicitness

If the rest of the sentence is implicit from context, it may end in the ga が, even though normally it would not.

For example, imagine two people talking. If one says someone did something, and the other is surprised by this fact, they may repeat "someone" plus the subject marker, expressing that's the part they're surprised about, skipping repeating the rest of the sentence.

Tanaka-san ga ninja wo koroshita.
田中さんが忍者を殺した。
Tanaka killed a ninja.
Tanaka-san ga?!
田中さんが！？
Tanaka [did it]?! (HE was subject behind this feat?! As opposed to literally anyone else?!)

Similarly, the conjunction can translate to "though" if what was meant to come after it is implicit from context.

kare wa kanji ga yomenai
彼は漢字が読めない
As for him, kanji isn't able-to-read.
He can't read kanji.
watashi wa yomeru ga
私は読めるが
As for me, [it] is able-to-read, though.
I can read [it], though.

Due to Omission

Sometimes, the rest of the phrase isn't simply implicit due to repetition, it's also been omitted and never been explicitly said anyhow.

Since nobody has said it, you might wonder how do you know what it's supposed to mean, when half the phrase is nowhere to be found?

In this case, it can either be inferred from context, even without words, or maybe you aren't supposed to know it.

For example: imagine a king, sitting on his throne, being all royal, and stuff, when through the hall, walks a dude, holding on his arms, in front of his chest, a pillow, on which is something, covered by a veil. He stands before the king, his fingers reaching for the veil. He unveils the something, showing it to the king, and the king, seeing the thing, exclaims:

kore ga!
これが！
This!

THIS WHAT?!

Clearly, we have no idea what in the world could have possibly been unveiled in front of the king's eyes. And given that I just made that up on spot, I, the author, don't know it either. It could be anything.

The point is that this "this," kore これ, is marked as the subject, and the rest of the phrase, although omitted, would have it as the subject. That's only hint you got.

For example, you could imagine what the king was going to say would be:

kore ga sugoi!
これが凄い！
This is amazing!

As a conjunction, when ga が can ends the sentence with omission, it's usually because what's supposed to come after it is supposed to be "what about it?"

This happens when person A asks person B if they can do something, or if they are something, or whatever, and B says, "well, yeah, so what?"

kanji ga yomeru ka?
漢字が読めるか？
Is kanji able-to-read?
Can [you] read kanji?
watashi wa yomeru ga?
私は読めるが？
As for me, [it] is able-to-read, but?
I can read [it], but?
- What are you going to do with this information?
- Why are you asking me this?
- ~~Who are you? Who do you work for?~~

Compounds

The ga が particle can be combined with the no の nominalizer, which turns verbs and adjectives into nouns, forming the compound noga のが.

oishii keeki ga tabetai
美味しいケーキが食べたい
To eat "the cake [that] is delicious" is want.
[I] want to eat "the cake [that] is delicious.
[I] want to eat the delicious cake.
oishii no ga tabetai
美味しいのが食べたい
To eat "one [that] is delicious" is want.
[I] want to eat "one [that] is delicious."
[I] want to eat a delicious one.
[I] want to eat the delicious one.
[I] want to eat the delicious ones.

hashiru no ga tanoshii
走るのが楽しい
The act [that is] "to run" is fun.
To run is fun.
Running is fun.

As usual, the no の nominalizer becomes nano なの when it's qualified by the predicative da だ copula, as it becomes the attributive na な copula in a relative clause, forming the compound nanoga なのが.

kirei da
綺麗だ
Is pretty.
kirei na neko ga suki
綺麗な猫が好き
"A cat [that] is pretty" is liked.
[I] like cats [that] are pretty.
[I] like pretty cats.
kirei na no ga suki
綺麗なのが好き
"One [that] is pretty" is liked.
[I] like the one [that] is pretty.
[I] like the pretty one.
[I] like the pretty ones.

With the conjunction ga が, you can use the copula in its predicative form, ending up with daga だが.

shujinkou ga baka da
主人公がバカだ
The main-character is stupid.
baka na shujinkou
バカな主人公
A main-character [that] is stupid.
A stupid main-character.
baka da ga tsuyoi
バカだが強い
Is stupid, but is strong.

This also works with the polite copula desu です. This is seen in the names of some series, like:

Kumo Desu ga, Nanika?
蜘蛛ですが、なにか？
[I] Am a Spider, But [Is There] Something [You Want From Me]?
[I] Am a Spider, [So What]?
Sakamoto Desu ga?
坂本ですが？
[I] Am Sakamoto, But [Is There Something You Want From Me]?

You can use the predicative da だ with the no の nominalizer to assert another phrase ending in da だ, in which case the subordinate da だ becomes na な, and you get nanoda なのだ.

Therefore, the compounds nanodaga なのだが and nanodesuga なのですが also exist.

The no の nominalizer can be contracted to the n ん particle before the predicative copula.

Therefore, the compounds nandaga なんだが and nandesuga なんですが also exist.

baka na no da ga
バカなのだが
[He] is stupid, though.
baka na no desu ga
バカなのですが
(same meaning.)
baka nandaga
バカなんだが
(same meaning.)
baka nandesuga
バカなんですが
(same meaning.)

Genitive Case Marker

One less important function of the ga が particle is to mark a noun as in the genitive case. This is exactly the same function the no の particle has when it creates no の adjectives.

The main difference is that ga が is older and not used in normal Japanese anymore. It still shows up in a few words used in modern Japanese, and it's also part of names of things and people.

Possessive Marker

Just like no の, ga が can create possessive adjectives out of nouns through the genitive case. This notably happens in literally just one word:

waga 我が
My.
Our.
One's.

The possessive above is basically the same thing as:

watashi 私
I. Me.
watashi no 私の
My. Mine.

Except it's related to the first person pronoun ware 我 instead.

Some examples of how it's used:

waga kuni
我が国
Our country.
One's country.
waga kou
我が校
Our school.
One's school.
waga ko
我が子
Our child.
One's child. Someone else's own child. (i.e. sacrifice one's own child, that sorta stuff.)
waga hai
我が輩
I. Me.
- Literally "one's group."
- Same sense as kochira こちら is used to say "us."
- Also, same as senpai 先輩 being "early group,"i.e. "seniors."

In Names of Places and People

The same ga が particle is also found in names of places and people. In this case, it works like this: you have a place, like some "plains," and you qualify them with a noun, like "battlefield," and the family that lived there probably inherits that name or something like that.

Anyway, in such cases ga が can get spelled as ga ヶ instead. For example:

Senjougahara Hitagi
戦場ヶ原ひたぎ
(Bakemonogatari character.)
Senjou ga Hara
戦場が原
(in other words.)
Senjou no Hara
戦場の原
Battlefield Plains.
Plains of Battlefield.

Other characters with similar names include:

Yuigahama Yui
由比ヶ浜結衣
(from Oregairu.)
- Yui no Hama
  由比の浜
  Beach of Cooperation.
Kirigaya Kazuto
桐ヶ谷和人
(a.k.a. Kirito, from Sword Art Online.)
- Kiri no Ya
  桐の谷
  Paulownia Trees' Valley. (or something like that.)

In some cases, a place that was named in such manner long ago loses the ga が in modern spellings of its name. For example:

Akihabara
秋葉原
(a place.)
Akiha ga Hara
秋葉ヶ原
Autumn Leaves' Plains.
Plains of Autumn Leaves.