は and が are the eternal struggle for Japanese learners. Both can follow a subject, and many sentences work with either — but the nuance is completely different.
This article systematically covers every rule for は and が.
Identity Check: は = Topic, が = Subject
| は | が | |
|---|---|---|
| Type | Adverbial particle | Case particle |
| Function | Marks the topic — what we're talking about | Marks the subject — who does the action |
| Info type | Known/old information | New information, focus |
One dialogue makes the difference crystal clear:
A: 誰が田中さんですか。 (Who is Tanaka?) B: 私が田中です。 (I'm Tanaka.)
A doesn't know who Tanaka is → が (focus on "who"). B's answer "I" is new information → が.
The reverse:
A: 田中さんはどなたですか。 (As for Mr. Tanaka, who is he?)
A already knows Tanaka exists and wants to learn more → Tanaka is a known topic → は.
Memory tip: が answers "who/what"; は answers "how/what about it."
Rule 1: Question Word + が (Absolute Rule)
When a question word is the subject, only が works — never は:
| ○ | × |
|---|---|
| 誰が来た？ | ×誰は来た？ |
| 何が起きた？ | ×何は起きた？ |
| どちらがいい？ | ×どちらはいい？ |
And the answer also uses が:
Q: 誰がケーキを作った？ (Who made the cake?) A: ヨウコが作った。 (Yoko did.)
Rule 2: First Appearance = が
When something appears for the first time in a conversation or narrative, use が:
| Sentence | Note |
|---|---|
| バスが来た。 The bus came. | Bus just appeared → new info |
| 雨が降っている。 It's raining. | Reporting current phenomenon |
| 電話が鳴った。 The phone rang. | Sudden event |
These are momentary phenomena — you see/hear something and report it.
Once established as known, it switches to は:
バスが来た。そのバスはとても混んでいた。 The bus came. That bus was very crowded.
Rule 3: が Inside Relative Clauses
When a subject appears inside a clause modifying a noun, only が works:
| ○ | × |
|---|---|
| 友達が作ったケーキ | ×友達は作ったケーキ |
| 先生が言ったように | ×先生は言ったように |
| 彼が住んでいる家 | ×彼は住んでいる家 |
Why? は "cuts" the modification relationship — は splits a sentence into "topic" and "comment," but modifying clauses need to stay tightly connected to the noun.
先生が言ったように、それはとても素晴らしい論文です。 → As the teacher said, that's an excellent paper.
Rule 4: Different Subjects in Conditionals = が
In conditional clauses (たら/ば/と/なら) where the subjects differ, the first clause uses が:
| Sentence | Note |
|---|---|
| 先生が行けば、私も行きます。 | Different subjects (teacher vs me) |
| 雨が降った場合、21日に延期されます。 | Different subjects (rain vs event) |
If the subjects are the same, は is fine:
私は暇なら、行きます。 (If I'm free, I'll go.)
Rule 5: は for Contrast
Another core function of は is contrast — "A, well... (but B is different)":
| Sentence | Meaning |
|---|---|
| ビールは飲むが、酒は飲まない。 | Beer I drink, but sake I don't. |
| 刺身は食べない。 | Sashimi I don't eat. (implying other things I do) |
| いつもはありますが、今はありません。 | Usually there is, but now there isn't. |
When you see two は in one sentence, it's almost always contrast:
猫は好きだが、犬は苦手だ。 Cats I like, but dogs — not so much.
Rule 6: Negation Prefers は
In negative sentences, the negated element often takes は for emphasis:
| Affirmative | Negative |
|---|---|
| 全部が読めます。 Can read all. | 全部は読めません。 Can't read all of it. |
| お金がある。 Have money. | お金はない。 Money, well, I don't have. |
Negation + は = "this particular thing, no" — with a limiting or contrasting tone.
Rule 7: は Replaces が/を, Stacks on に/で/から
は can replace が and を, but stacks onto に, で, から, と:
| Replaces | Stacks |
|---|---|
| 猫が → 猫は (が disappears) | ここでは食べてはいけない (で + は) |
| 本を → 本は (を disappears) | 東京には行ったことがある (に + は) |
Stacking adds topicalization or contrast:
| Sentence | Nuance |
|---|---|
| ここで食べてはいけない。 | You can't eat here. (general rule) |
| ここでは食べてはいけない。 | Here you can't eat. (elsewhere maybe OK) |
Special: The Eel Sentence
Japanese has a famous pattern called the "eel sentence" (うなぎ文):
私はうなぎです。
This doesn't mean "I am an eel" — it's ordering at a restaurant: "For me, eel (please)."
は marks the topic (as for me), and です abbreviates the verb (I'll have). Perfectly natural in Japanese.
Double Subject: は and が Together
は and が can coexist — は marks the broad topic, が marks the subject or focus within:
| Sentence | Analysis |
|---|---|
| 象は鼻が長い。 | は = topic (elephants), が = subject (nose) |
| 私は日本語が分かる。 | は = topic (me), が = ability target (Japanese) |
The は...が pattern: Big topic は + small subject が + predicate. This is Japanese's unique double-subject structure.
Decision Flowchart
When in doubt, check in this order:
- Question word as subject? → が
- Inside a relative clause? → が
- Conditional with different subjects? → が
- First appearance / sudden phenomenon? → が
- Contrast, negation, topic explanation? → は
- None of the above? → Default to は (topic is more versatile)
Summary
- が = subject (who did it): after question words, inside clauses, different-subject conditionals, new info
- は = topic (speaking of...): known info, contrast, negation emphasis
- は replaces が/を but stacks onto に/で/から/と
- Negation prefers は (limiting nuance)
- 「象は鼻が長い」: は = big topic, が = small subject
- When truly unsure, default to は — it has broader applicability
Practice Questions
Q1. は or が: 「＿＿来ましたよ！」(The bus is here!)
Show answer
バスが来ましたよ！
The bus just appeared — it's new information / a sudden event → が.
Q2. は or が: 「先生＿＿言ったように、それはとても素晴らしい。」
Show answer
先生が言ったように
"先生が言った" is a clause modifying "ように" — subjects inside relative clauses must use が.
Q3. Why does 「ビールは飲むが、酒は飲まない」 use は twice?
Show answer
This is は for contrast. The two は put "beer" and "sake" in opposition: beer — I drink; sake — I don't. Two は in one sentence almost always signals contrast.