[karatinversion]

If the topic and subject are the same, just は is used, but there are many sentences where the two differ, eg. 「映画館は人が多かった」- “there were many people in the cinema”, where “people” is the subject and “cinema” the topic. Or 「ここはパンが売れる」- “they sell bread here”, where the topic is “here” and “bread” is the subject.