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Questions & Answers about hon wa yasui desu.
Why is は used after 本?
は is the topic marker. It tells the listener "as for the book..." and sets 本 as what we’re talking about. It doesn’t literally translate to “is,” but indicates that 本 is the topic of the sentence.
Why is there no separate word for “is” before 安い?
In Japanese, 安い itself is an i-adjective (ending in い) and can directly form the predicate. The copula です that follows simply adds politeness; there is no separate “to be” verb needed for descriptive adjectives.
What is the role of です here?
です is the polite copula. It functions like “is” in English but also raises the politeness level. In plain speech you can omit です (saying 本は安い), but in polite conversation you include です.
Why does 安い end with い, and what does that tell me?
Adjectives in Japanese fall into two major categories: i-adjectives and na-adjectives. 安い ends with い, so it’s an i-adjective. I-adjectives can directly modify nouns (e.g. 安い本, “a cheap book”) and can act as predicates without a verb.
Can I drop です and just say 本は安い?
Yes. 本は安い is the plain (casual) form, common in informal settings or writing. Adding です to make 本は安いです shifts it into polite speech.
Could I use が instead of は in this sentence?
You could say 本が安い if you want to emphasize that it’s the book (among other things) that’s cheap, or answer a question like “Which item is cheap?” But 本は安い makes a general statement about the book.
How would I turn this into a question?
Attach か to です to make 本は安いですか. That becomes “Is the book cheap?” in polite speech.
Why is word order 本 は 安い です and not like English “is cheap book”?
Japanese follows Topic–Comment or Subject–Object–Verb (SOV) order. Here you have Topic (本は), then comment/predicate (安いです). English is Subject–Verb–Object (SVO), so the adjective comes before the noun, but in Japanese predicates come at the end.