は

1. Origins, structure, and basic meaning

• Structure: Add は after the topic; the particle is pronounced わ.
• Basic usage: 私は毎朝お茶を飲みます。 states a habitual action with the speaker as topic.

2. Common pitfalls and similar expressions

• A topic need not be the subject
  • In この本は昨日読みました, the book that was read is the topic. Do not always interpret the phrase before は as the person acting.
• Contrast and other particles
  • 今日は行きますが、明日は行きません contrasts two days. A particle such as に can remain when topical or contrastive は is added, as in 学校には行きます.