は vs が: A Practical Guide to Japanese Topic and Subject Particles

Almost every Japanese learner asks the same question sooner or later: when do I use は and when do I use が? Textbooks often answer with "は marks the topic and が marks the subject," which is true but not very helpful when you are staring at a blank sentence. This guide from the POMODIARY team breaks the difference into a handful of practical rules, each with example sentences and translations, followed by the mistakes we see learners make most often.

A quick note on pronunciation: the topic particle は is written with the kana for ha but pronounced wa.

The core idea in one sentence

は tells the listener what you are going to talk about; が points to which thing, specifically, does or is something.

Think of は as setting the stage and が as shining a spotlight. Most of the rules below follow from that picture.

Rule 1: は introduces a topic, then you comment on it

私は学生です。 As for me, I am a student.
東京は大きいです。 Tokyo is big.
この本は面白かった。 This book was interesting.

The part before は is the frame. Everything after it is a statement about that frame. The topic does not even need to be the grammatical subject:

象は鼻が長い。 Elephants have long trunks. Literally: as for elephants, the trunk is long.
昨日は雨でした。 Yesterday, it rained. (As for yesterday, it was rain.)

The elephant sentence is famous among Japanese grammarians precisely because it shows both particles at once: 象 is the topic, 鼻 is the subject of 長い.

Rule 2: が marks new information; は marks known information

When something enters the conversation for the first time, it often takes が. Once it is established, it switches to は.

昔々、おじいさんがいました。おじいさんは山に住んでいました。 Once upon a time, there was an old man. The old man lived in the mountains.

This pattern appears in many Japanese folk tales. The first mention uses が because the old man is new; after that he is the topic.

The same applies to everyday speech:

あ、猫がいる！ Oh, there's a cat!
その猫は誰の猫？ Whose cat is that?

Rule 3: Question words take が, and so do their answers

Question words like 誰 (who), 何 (what) and どれ (which) cannot be topics, because a topic is something already known. They take が.

誰が来ましたか。 Who came?
田中さんが来ました。 Tanaka came.

Answering with は here (田中さんは来ました) sounds odd, or implies contrast: Tanaka came, at least, but others did not.

どれが一番安いですか。 Which one is the cheapest?
これが一番安いです。 This one is the cheapest.

Rule 4: が for exhaustive focus ("it is X that...")

Because が spotlights, it can mean "X and nobody else" or "X, as opposed to anything else."

私が払います。 I will pay. (It is me who will pay, not you.)
私は払います。 I will pay. (As for me, I will pay; maybe others will not.)

A common situation: someone asks who is in charge, and you say 私が担当です (I am the one in charge).

Rule 5: は for contrast

は can contrast one thing with another, either explicitly or by implication.

肉は食べますが、魚は食べません。 I eat meat, but I don't eat fish.
日本語は話せます。 I can speak Japanese (implying: but maybe not other languages).
今日は暇です。 Today I'm free (implying: other days I am not).

This is why は often appears in negative sentences: 今日は行きません suggests "today, at least, I am not going."

Rule 6: Inside subordinate clauses, use が

In a clause that describes a noun or sits inside a larger sentence, the subject normally takes が, not は.

母が作った料理はおいしい。 The food my mother made is delicious.
雨が降ったら、行きません。 If it rains, I won't go.
彼が来たとき、私は寝ていました。 When he came, I was asleep.

In the last example, 彼 is inside the "when" clause and takes が, while 私 is the topic of the whole sentence and takes は. Putting は inside the clause (彼は来たとき) is a classic learner error.

Rule 7: Certain predicates take が for their object

With some adjectives and verbs, the thing liked, wanted, understood or possible is marked with が.

私は寿司が好きです。 I like sushi.
水が欲しい。 I want water.
日本語がわかります。 I understand Japanese.
ピアノが弾けます。 I can play the piano.
頭が痛い。 My head hurts.

Here は usually marks the person (the topic), and が marks the object of liking, wanting or ability. Using を with 好き is a common mistake; with potential verbs like 弾ける, both が and を are heard, but が is the textbook standard.

Summary table

Situation	Particle	Example
Setting a topic to comment on	は	私は会社員です。
Introducing something new	が	犬がいます。
Talking about something already mentioned	は	その犬は大きいです。
Question words and their answers	が	誰が来た？山田さんが来た。
"It is X who/that..."	が	私がやります。
Contrast	は	魚は食べません。
Subject inside a modifying or conditional clause	が	友達が書いた本
Object of 好き, 欲しい, わかる, potential verbs	が	猫が好きです。
Describing natural phenomena as you notice them	が	雨が降っている。

Common learner errors

Using は everywhere

Learners who first master 私は〜です often put は on every subject. 雨は降っています sounds like you are contrasting rain with something else. When you simply notice something happening, use が: 雨が降っています (It is raining).

Using は after question words

何は好きですか is wrong. Use 何が好きですか (What do you like?).

は inside relative clauses

私は買った本 does not mean "the book I bought." It is 私が買った本. You can then add a topic: 私が買った本は高かった (The book I bought was expensive).

Overusing 私は

Japanese drops subjects that are clear from context. Saying 私は in every sentence sounds stiff or even self-centred. Once the topic is established, leave it out: 私は学生です。大学で経済を勉強しています。

Translating "is" directly

English "is" does not map to either particle. Ask instead: am I setting a topic, or pointing to a specific thing?

How to practise

Rules only become instinct through lots of exposure and production. Three exercises we recommend:

Particle-blank drills. Take sentences from your reading, remove は and が, and fill them back in a day later. Then check, and for each error, name the rule you broke.
Retell a short story. Describe a picture or a short scene in Japanese. Introduce each new character with が and refer back with は.
Read natural text and annotate. In any article or post, highlight every は and が and decide which rule explains each one.

Typing practice is useful for the first exercise, because it forces you to choose a particle every time rather than skimming past it. FlowType.AI has a fill-in (Cloze) mode that hides parts of a sentence, plus AI explanations you can ask about a particle choice. For real-world examples, FlowType Grammar Lens can break down Japanese posts on X so you can see how native writers use は and が in casual writing.

Final advice

There are cases where both particles are grammatical and the difference is a matter of nuance, and even native speakers sometimes cannot explain their choice. Do not let that stop you. If you apply the seven rules above, you will be right in the large majority of everyday sentences, and the remaining subtleties will come with reading and listening over time.