The One-Sentence Answer
は marks the topic — what the sentence is about. が marks the subject — who or what performs or carries the state.
That sounds like a tidy distinction until you realise most sentences could take either. The difference is what the sentence is doing: は introduces or comments on something already in play; が identifies something as the answer.
The first is a neutral introduction. The second answers a question — probably "who is the student?" — and it would sound strange with no such question in the air.
What は Does
は sets the frame. Everything after it is a comment on that frame. It can replace が, を, and sometimes に in the topic position, which is why learners see it in places where the grammar suggests a different particle.
は creates contrast
Any element marked with は can imply a contrast with something else. ビールは飲みます suggests that beer is fine but something else is not. This implied contrast is one reason Japanese speakers use は sparingly when they do not intend to contrast.
は never appears inside a relative clause
When a clause modifies a noun, the subject takes が: 田中さんが書いた本 (the book Tanaka wrote). Using は there is a common and very visible error.What が Does
が marks the subject as new, identified, or exhaustive. It is the particle of answers, of existence, and of several verbs that describe states rather than actions.
The question-word rule
Question words cannot be marked with は. Ask 誰が, 何が, どれが — and answer with が. This is one of the few absolutely reliable rules in the pair.
Minimal Pairs Worth Memorising
Seeing the same sentence with both particles is the fastest way to internalise the difference.
The elephant sentence shows the classic topic-comment shape: は marks the topic (elephants), が marks what is being described within it (trunks). Japanese allows this nesting freely, which is why 私は頭が痛い works perfectly.
A Practical Decision Routine
The beginner rule of thumb
Start sentences with は, and use が for answers, existence and question words. That single heuristic produces natural Japanese in most everyday situations, and you can refine it later.
Common Mistakes
Sentence-final が is a different thing entirely — a conjunction meaning "but". Do not confuse it with the subject marker.
Practice
- ___ が学生ですか。（who is the student?）
- 私 ___ 学生です。（neutral introduction）
- 冷蔵庫にビール ___ あります。
- 日本語 ___ 少しわかります。
- 彼 ___ 書いた小説を読みました。
For the full particle inventory, read the Japanese particles guide. If sentence order is still uncertain, start with Japanese sentence structure.
FAQ
What is the difference between は and が in one sentence?
は marks the topic and が marks the grammatical subject. In 象は鼻が長い, は introduces the topic (elephants) and が identifies what is being described within it (their trunks). Japanese allows this topic-comment structure routinely.
Can I always use は instead of が?
No. Question words require が, existence verbs like ある and いる require が, and relative clauses cannot take は. Using は everywhere produces understandable but noticeably unnatural Japanese.
Why does 好き take が?
Because Japanese treats likes and dislikes as states rather than actions: the thing liked is the subject of the state, so it takes が. The same logic applies to わかる, できる and ほしい.
Is が always for new information?
As a rough guide, yes: が introduces or identifies, while は assumes the listener already knows what is being talked about. But が also appears in fixed patterns with particular verbs, which is why the verb list matters as much as the information structure.