〜が — Subject Marker

〜が

Property	Value
Pattern	が
JLPT Level	N5
Type	particle
Formality	Neutral

Meaning

The particle が (ga) is one of the most fundamental particles in Japanese. It has two primary roles:

Grammatical subject marker — it marks who or what performs the action or is in the state described by the predicate.
New information marker — it introduces a subject that is being mentioned for the first time, or highlights the subject as the answer to an implicit "who/what" question.

が is also required (not optional) after the subject of certain predicates, including:

あります / います (existence: there is / there are)
わかる (to understand)
できる (to be able to, to exist as a possibility)
好き (like) and 嫌い (dislike)

Structure Formula

[Noun] + が + [Predicate]

The noun before が is the grammatical subject of the sentence.
が directly precedes the predicate (verb, adjective, or noun + copula).

Example Sentences

Japanese	Romaji	English
猫(ねこ)がいます。	Neko ga imasu.	There is a cat.
田中(たなか)さんが来(き)ました。	Tanaka-san ga kimashita.	Mr. Tanaka came.
日本語(にほんご)がわかります。	Nihongo ga wakarimasu.	I understand Japanese.
私(わたし)はピザが好(す)きです。	Watashi wa piza ga suki desu.	I like pizza.
空(そら)が青(あお)い。	Sora ga aoi.	The sky is blue.

は vs. が Comparison

This is one of the most discussed distinctions in Japanese grammar. A brief guide:

Feature	は (topic marker)	が (subject marker)
Function	Marks the topic of the sentence	Marks the grammatical subject
Information role	Refers to known / established information	Introduces new or focused information
Scope	Sets the frame for the whole sentence	Emphasizes the noun it marks
Example	猫は魚を食べる。(As for the cat, it eats fish.)	猫が魚を食べる。(It is the cat that eats the fish.)

Rule of thumb: Use は when the subject is already known or you are making a general statement. Use が when identifying who or what, or when using predicates that require が (好き, わかる, できる, etc.).

Common Mistakes

Replacing が with は after 好き / 嫌い: ❌ 私はすしは好きです。→ ✓ 私はすしが好きです。 Explanation: The thing you like is marked with が, not は. Using は here changes the nuance to contrast (I like sushi but not other things).
Dropping が with います / あります: ❌ 本あります。→ ✓ 本があります。 Explanation: Existence predicates require が to mark what exists. Dropping the particle is too casual and can sound ungrammatical.
Using が instead of は for general statements: ❌ 犬が動物です。(introducing a fact about dogs in general) → ✓ 犬は動物です。 Explanation: For general definitions or facts about a known topic, は is the natural choice. が would imply "it is the dog (not something else) that is an animal," which sounds awkward.
Confusing subject and object: ❌ 私がりんごを食べます。(correct only when answering "who eats the apple?") vs ✓ 私はりんごを食べます。(general statement: I eat the apple) Explanation: が on the subject strongly focuses attention on that noun. Use it deliberately, not as a default substitute for は.