Quick Answer
は (wa) marks the topic of the sentence — what you are talking about, often something already known or being contrasted. が (ga) marks the grammatical subject — the doer of an action or the entity that carries a property, often introducing new or emphasized information. Both can translate as "subject" in English. Swap them, though, and you either change the meaning entirely or produce something no native speaker would say.
Comparison Table
| Feature | は (wa) | が (ga) |
|---|---|---|
| Grammatical role | Topic marker | Subject marker |
| Information type | Known / shared information | New / emphasized information |
| Contrast | Yes — implies contrast with others | No contrast implied |
| Focus | Falls on the predicate (what is said about the topic) | Falls on the subject (who or what) |
| In questions | Asks about the predicate | Asks about the subject / identifies who |
| Subordinate clauses | Cannot replace が inside relative clauses | Used inside relative/subordinate clauses |
| Existential sentences | Describes topic's location | Announces existence of something |
| Ability / desire / emotion | Rarely used as subject marker here | Required with できる, ほしい, 好き, etc. |
Detailed Explanation
When to use は
は sets up the topic — typically something both speaker and listener already know, or something being reintroduced into the conversation. Think of it as flagging: "As for X, ..."
- Established topics: Once a noun has been introduced, は marks it as the running topic of the discourse.
- Contrast: は carries an implicit contrast. 「私はビールを飲みます」 can imply "I (for my part, unlike others) drink beer."
- General truths and definitions: 「犬は動物です」 — "Dogs are animals" (universally true, no particular dog).
- Negatives and questions about the predicate: は naturally frames what is being denied or asked about.
When to use が
が identifies or introduces the subject. Reach for it when the subject is new information, or when you want to put the spotlight on who or what is performing an action.
- New information / first mention: When something appears for the first time in the conversation, が introduces it.
- Identification answers: 「だれが来ましたか」→「田中さんが来ました」 — が pinpoints who.
- Relative clauses: Inside a subordinate clause, が (not は) marks the subject: 「私が作った料理」 — "the dish that I made."
- Stative predicates — ability, desire, like/dislike, emotion: Verbs and adjectives such as できる, ほしい, 好き (な), 嫌い (な), わかる, and ある require が for their object/subject: 「日本語がわかります」.
- Existential sentences announcing something: 「猫がいます」 — "There is a cat (over there)" presents the cat as new information.
Example Pairs
Pair 1 — Introducing vs. Continuing
猫がいます。その猫は白いです。
Neko ga imasu. Sono neko wa shiroi desu.
There is a cat. The cat is white.
が introduces the cat as new information; は picks it up as the established topic in the next sentence.
Pair 2 — Focus on Subject vs. Predicate
田中さんが来ました。
Tanaka-san ga kimashita.
It was Mr. Tanaka who came. (identifies who)
田中さんは来ました。
Tanaka-san wa kimashita.
Mr. Tanaka came. (focus on the fact that he came — possibly implying others didn't)
Pair 3 — Question & Answer with Identification
だれが先生ですか？
Dare ga sensei desu ka?
Who is the teacher? (asking to identify the subject)
先生はだれですか？
Sensei wa dare desu ka?
As for the teacher, who is it? (topic already established; asking about the predicate)
Pair 4 — Like / Dislike (stative predicate)
私は寿司が好きです。
Watashi wa sushi ga suki desu.
I like sushi. (私 is topic; 寿司 is subject of 好き)
❌ 私は寿司は好きです。
Watashi wa sushi wa suki desu.
(Unnatural unless contrasting sushi with something else: "I like sushi, but not sashimi.")
Pair 5 — Existential: New vs. Known Location
公園に犬がいます。
Kōen ni inu ga imasu.
There is a dog in the park. (announcing the dog's existence)
犬は公園にいます。
Inu wa kōen ni imasu.
The dog is in the park. (we already know the dog; we're stating where it is)
Pair 6 — Ability with できる
彼女はピアノができます。
Kanojo wa piano ga dekimasu.
She can play the piano. (彼女 is topic; ピアノ is subject of できる)
❌ 彼女はピアノはできます。
Kanojo wa piano wa dekimasu.
(Contrastive only: "She CAN do piano [but not guitar]." Otherwise unnatural.)
Pair 7 — Relative Clause (subordinate clause)
私が書いた手紙
Watashi ga kaita tegami
The letter that I wrote (が required inside the relative clause)
❌ 私は書いた手紙
Watashi wa kaita tegami
(Ungrammatical — は cannot mark the subject inside a relative clause)
Pair 8 — Contrast with は
私は行きます。
Watashi wa ikimasu.
I will go. (possibly: I will go, even if others won't — contrastive nuance)
私が行きます。
Watashi ga ikimasu.
I will go. (emphasis: it is I who will go — identifying the subject)
Common Patterns
| Pattern | Correct particle | Example | Note |
|---|---|---|---|
| Stative adjective: 好き・嫌い・上手・下手 | が (for the object) | 音楽が好きです | が marks what you like/dislike |
| Ability: できる・わかる | が (for the object) | 英語ができます | が marks the skill/language |
| Desire: ほしい | が (for the desired thing) | 水がほしい | が marks the desired object |
| Existence: ある・いる (new info) | が (for the existing thing) | 問題がある | が announces existence |
| Relative clause subject | が (never は) | 彼が作った料理 | は not permitted here |
| Contrast (explicit or implied) | は | コーヒーは飲みますがお茶は飲みません | は highlights the contrast |
| General / universal statements | は | 人間はいつか死ぬ | は for definitions/facts |
| Answer to だれが / なにが question | が (in the answer) | だれが→山田さんが | が identifies the subject |
Common Mistakes
Mistake 1 — Using は inside a relative clause
「私は作った料理」 sounds plausible to beginners but is ungrammatical. Inside a relative clause, は cannot mark the subject — が is the only option: 「私が作った料理」.
Mistake 2 — Using は with 好き / できる / わかる
「日本語はわかります」 works only when drawing a contrast — say, "Japanese I understand, but not Chinese." Drop the contrast, and が is the natural choice: 「日本語がわかります」.
Mistake 3 — Treating both particles as interchangeable "subject markers"
「だれは来ましたか」 is flat-out wrong. Question words like だれ and なに that stand in for the subject always take が — は is simply not allowed after them.
Mistake 4 — Forgetting the contrastive weight of は
「私はビールは飲みます」 — the double は — sends a strong contrastive signal: "Beer, yes; other things, maybe not." Most learners add that second は carelessly, unaware of the extra weight it puts on ビール.
Mistake 5 — Using が for re-introduced topics
が keeps drawing attention to the subject as something new or noteworthy. When a noun is already established in the conversation, repeated が sounds over-emphatic. After the first mention, switch to は — or drop the noun entirely, as Japanese often does.
Related Articles
- に vs で — Location Particles (Comparison X vs Y)
- は vs も — Topic vs Also (Comparison X vs Y)
- から vs ので — Because (Comparison X vs Y)
- に vs へ — Direction (Comparison X vs Y)
- だけ vs しか — Only (Comparison X vs Y)
- と vs や — And (Listing) (Comparison X vs Y)
Quick Quiz
Fill in the blank with は or が.
- A: だれ___先生ですか？ B: 山田さん___先生です。
Answer
A: が — B: が (identifying who; answer mirrors the question structure)
Answer
First blank: が (inside relative clause) — Second blank: は (established topic, stating its location)
Answer
First blank: は (topic) — Second blank: は (contrastive: good at math, but bad at English)