が

が goes after a noun and marks it as the subject: the one that is there, the one that does something, the one a description is about. You meet it first with あります and います, where it marks what is there.

は or が

は sets up something already known and the news comes after it. が marks the noun itself as the news.

For the same reason, something mentioned for the first time usually takes が, and once it is known it takes は.

Question words take が

When "who", "what" or "which" is the subject of a question, it takes が, and the answer keeps が on the word that replaces it. In that position a question word does not take は.

• × だれは来ますか → だれが来ますか

Usage notes

These go beyond marking what is there and who does something.

With 好き, 嫌い and words like them

The thing you like or dislike takes が. So does the thing you want (ほしい), understand (わかります) or are good at (じょうず上手).

English makes these things objects, which pulls learners towards を.

• × 音楽を好きです → 音楽が好きです

Saying what you see

A plain report of what is in front of you – the weather, something arriving – puts が on the subject.

は for the whole, が for the part

To describe one part or one side of something, the whole takes は and the part takes が.

が between two sentences

A が at the end of a clause is a different word, meaning "but".