Nihongo Desk日语课桌

How to choose は or が: topic, focus, and clause structure

Practice identification, contrast, and noun modifiers without treating old versus new information as a universal rule.

Separate the topic from the participant in a statement

As a first approach, は establishes a topic or contrast, while が identifies who or what has an action, state, or property. 「この店は安いです。」 makes this shop the topic. 「あの店が安いです。」 can identify that shop in response to “Which is inexpensive?” Do not choose solely by the position of an English subject.

“は is old information; が is new information” helps with some introductions but is not a universal rule. A new person can become a topic; a known person can be identified with が. Check the preceding question, the intended focus, and the grammatical structure. An isolated sentence may permit both with different emphasis.

Use the question to identify the focus

「だれが予約しましたか。」 (Who made the reservation?) normally invites 「私が予約しました。」 (I did.) Here が identifies the requested person. If the question is 「林さんは何をしましたか。」 (What did Lin do?), 「林さんは席を予約しました。」 continues the established topic. Do not mechanically put は after a word asking who.

Once participants and actions are clear, omission may be natural: 「予約しました。」 can be enough. Keep complete sentences for comparison in a grammar exercise, but do not require repeated 「私は」 in real interaction.

Example

Original scenario: three people arrange a meal. A asks 「だれが店を選びましたか。」 (Who chose the restaurant?) B answers 「由美さんが選びました。」 (Yumi did.) The person is the focus.

Next, A asks 「由美さんは何を予約しましたか。」 (What did Yumi reserve?) B says 「由美さんは個室を予約しました。」 (Yumi reserved a private room.) Yumi is now the topic; the room is the added information.

Contrast and topic–subject combinations

「コーヒーは飲みますが、お酒は飲みません。」 means “I drink coffee, but not alcohol.” The two は phrases contrast drinks. The middle が joins clauses with a contrastive meaning; it is not the subject-marking particle. Position matters when identifying function.

In 「私は魚が好きです。」 (I like fish), 私は provides the topic and 魚が belongs with 好き. Having は does not remove the need for が, and が cannot always be replaced by を. Learn preference, ability, and existence patterns with their particles. 「魚は好きです」 can contrast fish with other foods, changing the emphasis.

Do not replace が mechanically inside noun modifiers

In 「友達が作ったケーキを食べました。」 (I ate the cake my friend made), 「友達が作った」 modifies ケーキ and が identifies the maker. This is a useful beginner pattern. The fact that the friend is known does not call for a mechanical replacement with は. Contrastive は is possible in some modifier constructions, but that is a different function.

Compare 「友達はケーキを作りました。」 (My friend made a cake). The first sentence embeds “the cake my friend made” in a larger statement; the second directly takes the friend as its topic. Clause structure matters, not just whether a name has appeared before.

Add context to a particle exercise

Write the question, response, and intended focus. Explaining a choice is more reliable than an old/new mnemonic. Where both work, supply a context for each. Our verified Minna Beginner Lesson 9 offers topic–が patterns and Lesson 10 offers existence patterns; these lessons do not claim to cover every advanced boundary on this page.

The exercise fixes the context and explains the expected focus. Afterwards substitute your own people or objects. In longer sentences, identify clause boundaries before deciding on contrast.

Check your understanding

Answer 「だれが窓を開けましたか」 with 「美奈さん（　）開けました」, identifying the person who opened the window.

Make the explicit contrast “I drink tea, but not coffee”: 「お茶（　）飲みますが、コーヒー（　）飲みません」.

Choose は or が for the ordinary noun modifier “the book my older sister bought”: 「姉（　）買った本」.

Explanation

Use が: 「美奈さんが開けました。」. The question asks who; は would establish Mina as a topic or introduce contrast, rather than preserve the specified focus.

Both blanks take は. They contrast two drinks; the middle が connects clauses and has another function.

Use が to identify the buyer. A known person does not automatically require は inside an ordinary modifier. Special contrastive contexts are a separate issue.

Sources