は (wa) and が (ga) are both often translated as "is" or "the subject," but they do different jobs. Once you see the pattern, the confusion fades.
は marks the topic
Think of は as "as for ~." It introduces what the sentence is about, or sets up contrast.
- 私は学生です。 → "As for me, I'm a student."
- 今日は晴れです。 → "As for today, it's sunny."
The information after は is the point: what about me? → I'm a student.
が marks the subject (the new information)
が identifies who or what does something — it's the answer to a question, or it highlights something specific.
- 誰が来ましたか？ → "Who came?"
- 田中さんが来ました。 → "Tanaka came."
With が, the subject itself is the focus.
Side by side
Same words, different feeling:
- 山田さんは先生です。 → "Yamada (you know, the one we're talking about) is a teacher."
- 山田さんが先生です。 → "Yamada is the one who is the teacher."
When が is required
A few patterns always take が:
- Existence: 部屋に猫がいます。 → "There's a cat in the room."
- Likes/desire: 犬が好きです。 → "I like dogs."
- Subordinate clauses: 私が買った本 → "the book I bought"
A simple rule of thumb
Use は when you're explaining or contrasting something already known. Use が when you're identifying, presenting new information, or stating something neutral about the subject. When in doubt, は for the main topic is usually safe.
See it in real sentences
Rules help, but pattern-matching against real text is how it sticks. Paste any sentence into Shiritai and every particle is labeled and explained in context.