Learn Hardcore Japanese: watasi ha tomodati ni hon wo kaesimasu.

は is the topic‐marker, so 私は means “as for me.” It sets 私 up as what the sentence is about. By contrast, が is a subject‐marker that often introduces new or emphasized information. In this case you aren’t emphasizing “I” as new info—you’re just stating what you (the topic) do.

How do you pronounce the particle は here?

When used as a topic marker, は is pronounced wa, not ha. The ha sound reading only applies when は is part of a word, not when it’s the standalone particle.

What is the function of the particle に after 友達?

The particle に marks the indirect object or the recipient of the action. Here, 友達に means “to (my) friend,” indicating who receives the returned book.

Why does 本 take the particle を?

を marks the direct object—the thing being acted upon. 本を返します literally means “(I) return the book,” so 本 (book) is the direct object of 返します.

Why is 返します placed at the end of the sentence?

Japanese follows a subject–object–verb (SOV) order. Verbs almost always go at the end, after all particles and objects, which helps listeners know when the action happens.

What level of politeness is 返します, and what’s its plain form?

返します is the polite -masu form. Its plain (dictionary) form is 返す. Use 返します in formal situations or with people you don’t know well; use 返す among close friends or family.

Is this sentence present tense or future tense?

In Japanese, the polite -masu form covers both present and future actions. Context decides whether it’s “I return” (habitually) or “I will return” (in the future).

Can 私は be omitted in everyday speech?

Yes. When the topic/subject is clear from context, Japanese often drops pronouns. So you could simply say 友達に本を返します if it’s obvious you’re the one doing the returning.

Could I use 返却します instead of 返します?

Yes. 返却します is a more formal or “business‐style” synonym of 返します. It’s often used in written notices, official announcements, or very polite contexts.