は vs が: the simple explanation

は (wa) and が (ga) confuse almost every learner, because both can sit after the "subject" of a sentence. There's a lot written about them, but for beginners, a few simple rules cover most sentences you'll meet.

The one-line version

は sets the topic: "as for X…". The new or important information comes after it. が points at X itself: X is the new or important information.

Compare:

In the first, the topic is "me", and the news is "Sophie". In the second, someone asked "which one of you is Sophie?", and the news is me.

Rule 1: question words take が

Question words like だれ (who), なに (what) and どれ (which) can't be the topic, because they're the unknown. So they take が, and so does the answer.

Rule 2: something new appearing takes が

When you first notice or mention something, use が. Once it's known, it usually becomes the topic with は.

Rule 3: likes, wants, skills and "having" take が

With 好き (like), きらい (dislike), じょうず (good at), ほしい (want), わかる (understand) and ある (have), the thing liked, wanted or had takes が. The person often takes は.

Rule 4: は for contrast

は can also mean "but as for this one…", contrasting one thing with another.

A quick test

Ask yourself: is the word what the sentence is about (は), or is it the answer or the news (が)?

• "What's this?" → これは なんですか (this is the topic; "what" is the unknown).
• "Which one is yours?" → どれが あなたのですか (the question word takes が).
• Talking about yourself → わたしは…