In short

は and が are not two answers to one question. が is a case particle - it says “this noun is the subject”. は is an information particle - it says “this piece is the frame, or the one I am singling out”, and it can sit on a subject, an object, a place, or on top of another particle. Once you stop treating them as rivals, three hard things become easy: which one goes inside a subordinate clause (always が), what a mid-sentence は implies (a contrast you did not say out loud), and how far a negation reaches.

The rule

Step 1 - See why the A1 formula breaks

“は = topic, が = subject” gets you through A1, but it predicts nonsense as soon as sentences get longer. Three facts kill it:

• They stack. 象は鼻が長いです。 (Zō wa hana ga nagai desu.) has both, in one clause. If they were rivals this could not exist.
• は goes on non-subjects. 本は読みました。 (Hon wa yomimashita.) - は is on the object. 東京へは行きます。 (Tōkyō e wa ikimasu.) - は is stacked on へ. が can never do either.
• They live on different axes. が answers which grammatical role?; は answers how does this fit the conversation? A noun can carry a case role and an information role at the same time - which is exactly what 象は鼻が長いです shows.

So the real question is never “は or が?” It is two separate questions: what case does this noun need, and am I framing or contrasting it.

Step 2 - Learn the four jobs

The classic description gives が two jobs and は two jobs. Almost every real sentence is one of these four.

• が, neutral description - you report an event as pure news, no frame at all. あ、雨が降っています。 (A, ame ga futte imasu.) - Oh, it’s raining. Typical of things you have just noticed, and of 〜ている, ある／いる, and change verbs.
• が, exhaustive listing - が picks one item out and asserts it, and no one else. This is why the answer to a wh-question takes が: 誰が行きますか (Dare ga ikimasu ka) -> 私が行きます。 (Watashi ga ikimasu.) = I’m the one going.
• は, thematic / generic - the frame, and by extension definitions and universal statements: 猫は魚が好きです。 (Neko wa sakana ga suki desu.) - Cats like fish (cats in general).
• は, contrastive - X, as opposed to something else. See Step 5.

Note the practical consequence of exhaustive-listing が: answering 誰が行きますか with 私は行きます does not answer the question. It only says as for me, I’m going - the questioner still does not know who the goer is.

Step 3 - Inside a subordinate clause, は is barred

This is the most mechanical rule in the lesson, and it is worth more than any nuance. は marks the topic of a whole sentence, so it cannot live inside a piece of one. In these environments the subject takes が:

• relative (noun-modifying) clauses - 私が読んだ本 (watashi ga yonda hon), never ×私は読んだ本 (lesson 18)
• conditional and temporal clauses - なら, たら, と, ば, とき, 前に: 雨が降ったら (ame ga futtara), 父が帰ったとき (chichi ga kaetta toki)
• reason clauses - ので, から: 雨が降ったので (ame ga futta node)
• nominalized clauses - こと／の: 彼が来ることを知りませんでした。 (Kare ga kuru koto o shirimasen deshita.)

Remember that the verb in all of these is plain, however politely the sentence ends: the default is ○雨が降ったので rather than 雨が降りましたので. (ので and から are the loophole - 行きますので、少々お待ちください is standard in formal announcements, and 〜ましたら belongs to that same polite register - but inside a relative clause the plain form is the only option, and before とき, ば and こと it is the ordinary choice.)

The one は you do sometimes meet inside a clause is the contrastive one, mostly in loosely attached clauses (から, けど, が): 時間はありませんが、行きます (Jikan wa arimasen ga, ikimasu). Inside a relative clause it is much rarer - you meet it in set negatives like お酒は飲まない人 (osake wa nomanai hito, someone who doesn’t drink) - and a thematic は is impossible there. Safe working rule: subordinate clause -> が.

Step 4 - が -> の inside a noun-modifying clause

Because the subject of a modifying clause is already locked to が, Japanese offers a second option there: replace it with の.

• 私が読んだ本 = 私の読んだ本 (watashi no yonda hon) - the book I read
• 背が高い人 = 背の高い人 (se no takai hito) - a tall person

Two limits, both frequently broken by learners:

1. Short clauses only. The の gets worse the further it stands from its verb. 私が昨日図書館で借りた本 is fine; ?私の昨日図書館で借りた本 is not.
2. No intervening を-object. If an object sits between the subject and the verb, の is blocked: ○私が毎日コーヒーを飲む店 / ×私の毎日コーヒーを飲む店.

の is slightly literary and compact - very common in fixed descriptive phrases like 背の高い人, 目の大きい子. It never works in a main clause: ×雨の降っています -> ○雨が降っています.

Step 5 - Contrastive は and the thing you did not say

Put は on any constituent and you invite the listener to fill in a contrast. Nothing is stated, but the implication is real:

• ビールは飲みません。 (Bīru wa nomimasen.) - I don’t drink beer - and the は quietly adds …though I might drink something else. Compare plain ビールを飲みません, which is a flat statement about beer only.
• 東京へは行きますが、大阪へは行きません。 (Tōkyō e wa ikimasu ga, Ōsaka e wa ikimasen.) - both halves marked; the contrast is now explicit.

Contrastive は stacks on へ, に, で, と, から - exactly the mechanics from lesson 4 - and it replaces が and を. When it appears mid-sentence rather than at the front, contrast is almost always the reading. It is also standard in the second half of an explicit contrast, which is why 〜が／〜けど sentences so often carry two は.

Step 6 - は controls the scope of negation

This is the highest-value payoff of the lesson. は decides what the negation targets. A thematic は-noun stays outside it, and the negation falls on the predicate; a contrastive は makes its noun the very thing denied.

• 全部食べませんでした。 (Zenbu tabemasen deshita.) - I ate none of it. The negation falls on the eating as a whole.
• 全部は食べませんでした。 (Zenbu wa tabemasen deshita.) - I didn’t eat all of it (I ate some). Contrastive は singles out 全部 as the target, so only “all” is denied.

The same logic separates these two:

• 私は行きません。 (Watashi wa ikimasen.) - I’m not going. The negation falls on 行く.
• 私が行くのではありません。 (Watashi ga iku no de wa arimasen.) - It isn’t me who’s going. Here 〜のではありません negates the whole nominalized clause, and the exhaustive が inside it is what gets denied.

Because negation and は cooperate so well, negative sentences drift naturally to は: お金はありません sounds more idiomatic than a bare お金がありません in most contexts. If a negative sentence feels stiff, try moving は onto the negated element.

Step 7 - Double-subject sentences, and one は per sentence

Topic + は + [ Subject + が + Predicate ] is the ordinary way to say what English says with have or a possessive: 日本は物価が高いです。 (Nihon wa bukka ga takai desu.) - Prices are high in Japan. The inner が-subject belongs to the predicate; the outer は frames it.

At the top level a Japanese sentence carries one は. If you find yourself writing a second one, check it: either it is contrastive, or one of them should be が, or the sentence should be two sentences.

Forms & patterns

The four jobs at a glance.

Where は may stand.

が -> の inside a modifier.

Scope of negation.

Examples

Common mistakes

• 私は読んだ本は面白かったです。 (Watashi wa yonda hon wa omoshirokatta desu.) -> 私が読んだ本は面白かったです。 (Watashi ga yonda hon wa omoshirokatta desu.) - a topic は cannot stand inside a relative clause; the clause-internal subject takes が. The outer は on 本 is the sentence’s real topic.
• 雨は降ったので、試合は中止になりました。 (Ame wa futta node, shiai wa chūshi ni narimashita.) -> 雨が降ったので、試合は中止になりました。 (Ame ga futta node, shiai wa chūshi ni narimashita.) - a ので clause is subordinate, so its subject is が. Only the main clause gets a topic.
• 私は行きます。 (Watashi wa ikimasu.) -> 私が行きます。 (Watashi ga ikimasu.) - as the answer to 誰が行きますか (Dare ga ikimasu ka, “who is going?”), this needs exhaustive-listing が. は only supplies a frame and leaves the question unanswered.
• 私の毎日コーヒーを飲む店 (watashi no mainichi kōhī o nomu mise) -> 私が毎日コーヒーを飲む店 (watashi ga mainichi kōhī o nomu mise) - が -> の is blocked once an を-object stands between the subject and the verb. Keep が in any clause that is not very short.
• 全部食べませんでした。 (Zenbu tabemasen deshita.) -> 全部は食べませんでした。 (Zenbu wa tabemasen deshita.) - if you mean “not all of it”, 全部 must be singled out as the target of the negation with は. Without は you have said you ate none.

Tips

• Ask two questions, not one. First: what case does this noun need (が, を, に, で)? Then: am I framing or contrasting it? If yes, は goes on top - replacing が／を, stacking after everything else. That order never fails.
• Front は frames, mid-sentence は contrasts. A は in the first slot is usually just the topic. A は that turns up later, especially on an object or stacked on a particle, is contrastive - and the listener is already waiting for the “but”.
• Subordinate clause, no exceptions worth learning: が. Relative clause, とき, たら, なら, ので, から, こと, の - all が. This one rule fixes more B1 sentences than any subtlety about topics, and it pairs with the plain-form rule: ○降ったので, with 降りましたので reserved for formal announcements.
• English has no は, so it hides in the stress. I don’t drink beer (falling on beer) is ビールは飲みません; a neutral “I don’t drink beer” is ビールを飲みません. When you cannot decide, say the English aloud and listen for which word is being singled out.