Short answer: は (read wa) marks the topic: what the sentence is about, usually something already known, like “as for Tanaka…”. が (ga) marks the subject when it is new or the focus of the sentence: “it is Tanaka who…”. Use は to say something about a topic, and が to answer “who?” or “what?”, to introduce something new, and with likes, abilities and existence.
A topic (主題 shudai) is the frame of the sentence; a subject (主語 shugo) is who or what performs the verb. They are often the same person, which is why the two particles feel alike.
は: “as for…”
は tells the listener “here is what I am talking about; now listen to what I say about it”. The topic is usually something both people already have in mind. Once a topic is set, Japanese often stops repeating it.
Kono hon wa omoshiroi desu.“This book is interesting.”Why:The book is in front of us, already known: は.
が: new information and “the one that…”
が marks the subject when it is the important new part of the sentence. A good test: if the English answer would stress the subject (“Tanaka came”), Japanese uses が.
A, ame ga futte imasu.“Oh, it’s raining.”Why:You have just noticed it: new information, so が.
ドアdoadoorがga(subject)開きましたakimashitaopened
Doa ga akimashita.“The door opened.”Why:Describing an event as it happens. With は it would mean “as for the door, it opened” (unlike something else).
電車denshatrainがga(subject)来ましたkimashitacame
Densha ga kimashita.“Here comes the train.”Why:An announcement of something new. Station announcements use が for this reason.
Question words always take が
A question word like 誰 (who) or 何 (what) is unknown by definition, so it can never be the topic. It takes が, and the answer keeps が on the new information.
A
誰darewhoがga(subject)来ましたかkimashita kacame?
Dare ga kimashita ka. · “Who came?”誰 is unknown, so が, never は.
B
田中さんTanaka-sanTanakaがga(subject)来ましたkimashitacame
Tanaka-san ga kimashita. · “Tanaka came.”Tanaka is the answer, the new part: が.
Dore ga ii desu ka. · “Which one would you like?”Literally “which one is good?”, used to offer a choice.
B
これkorethisがga(subject)いいですii desuis good
Kore ga ii desu. · “This one, please.”これが: this one, out of the choices.
は for contrast
は can also mark contrast: “this one, as opposed to that one”. Two は in one sentence almost always contrast two things. In speech the contrasted word is said a little more strongly.
Niku wa tabemasu ga, sakana wa tabemasen.“I eat meat, but not fish.”Why:Two は: meat versus fish. The が in the middle is a different word meaning “but”.
お酒osakealcoholはwa(contrast)ちょっとchottoa bit…
Osake wa chotto…“Alcohol is a bit… (I’d rather not).”Why:は suggests “other drinks are fine”: a soft way to decline one thing.
Likes, abilities, needs and existence: が
A group of everyday words takes が for the thing liked, understood, wanted or present. The person feeling or having it is the topic with は. Learn these as a set.
Pattern
Meaning
The が marks
~ ga suki desu
I like ~
the thing liked
~ ga kirai desu
I dislike ~
the thing disliked
~ ga wakarimasu
I understand ~
the thing understood
~ ga dekimasu
I can do ~
the skill
~ ga hoshii desu
I want ~
the thing wanted
~ ga arimasu
there is ~ / I have ~
the thing that exists
~ ga itai desu
my ~ hurts
the body part
は and が in the same sentence
With both particles, は gives the big topic and が the detail about it. The classic example is about an elephant.
Zō wa hana ga nagai.“Elephants have long noses.”Why:Topic: elephants. Subject of “long”: the nose.
私watashiIはwa(topic)日本語nihongoJapaneseがga(object of liking)好きですsuki desuis liked
Watashi wa nihongo ga suki desu.“I like Japanese.”Why:The person who likes takes は; the thing liked takes が.
象は鼻が長い does not mean the elephant is long: it means that, as for elephants, the nose is long. The same pattern describes people: 姉は目がきれいです, “my sister has beautiful eyes”.
Inside a clause, the subject takes が
When a smaller sentence sits inside a bigger one, such as a description before a noun or an “if” or “when” clause, its subject takes が, not は. は belongs to the whole sentence.
Haha ga tsukutta kēki wa oishii.“The cake my mother made is delicious.”Why:母が is inside the description of the cake; は marks the topic of the whole sentence.
雨amerainがga(subject)降ったらfuttaraif it falls行きませんikimasenwon’t go
Ame ga futtara, ikimasen.“If it rains, I won’t go.”Why:Subject of the “if” clause: が.
Tanaka-san ga kita toki, watashi wa nete ita.“When Tanaka came, I was asleep.”Why:Two subjects: が inside the 時 clause, は for the main sentence.
Negatives like は
Negative sentences very often use は, because saying what is not true usually implies a contrast: “not this one (but something else)”. The は replaces が or を.
The other が: “but”
A second, unrelated が joins two sentences and means “but”, or softens an opening. It follows a verb, adjective or です, never a bare noun, which is how you tell it apart from the subject marker.
は and が in a story
The opening of the folktale 桃太郎 (Momotarō) shows the pattern perfectly: new characters are introduced with が, then talked about with は.
昔々mukashi mukashilong, long agoおじいさんojiisanan old manとtoandおばあさんobāsanan old womanがga(subject)いましたimashitathere were
Mukashi mukashi, ojiisan to obāsan ga imashita.“Long, long ago, there lived an old man and an old woman.”Why:First mention: が introduces them.
おじいさんojiisanthe old manはwa(topic)山yamamountainへeto柴刈りshibakarigathering firewoodにnifor
Ojiisan wa yama e shibakari ni,“The old man went to the mountain to gather firewood,”Why:Now known: は.
おばあさんobāsanthe old womanはwa(topic)川kawariverへeto洗濯sentakuwashingにnifor行きましたikimashitawent
obāsan wa kawa e sentaku ni ikimashita.“and the old woman went to the river to do the washing.”Why:Two は contrast who went where.
が for “it’s X, and only X”
が can single out one answer from a set: “X (not anyone else)”. Stress falls on the word before が. With は the same sentence would describe X instead.
私watashiIがga(it is…)田中TanakaTanakaですdesuam
Watashi ga Tanaka desu.“I’m Tanaka (the one you’re looking for).”Why:Answering “which of you is Tanaka?”.
私watashiIはwa(topic)田中TanakaTanakaですdesuam
Watashi wa Tanaka desu.“I’m Tanaka.”Why:Simply introducing yourself.
Check yourself: は or が?
Decide which fits, then open the answer.
Gap 1誰（ ）来ましたか。dare ( ) kimashita kaShow answer
が: question words always take が.
Gap 2私（ ）学生です。watashi ( ) gakusei desuShow answer
は: saying something about yourself.
Gap 3あ、雨（ ）降ってきた。a, ame ( ) futte kitaShow answer
が: something you have just noticed.
Gap 4私は犬（ ）好きです。watashi wa inu ( ) suki desuShow answer
が: the object of 好き.
Gap 5肉は食べますが、魚（ ）食べません。niku wa tabemasu ga, sakana ( ) tabemasenShow answer
は: contrast with meat.
Gap 6母（ ）作った料理は美味しい。haha ( ) tsukutta ryōri wa oishiiShow answer
が: subject inside a description.
Which one? A quick guide
When in doubt, ask what the sentence is for.
はSaying something about a known topic私は学生です。
はContrasting two things肉は食べますが、魚は食べません。
がAnswering who, what or which田中さんが来ました。
がReporting something new you see or hearあ、雨が降っています。