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Questions & Answers about Эта книга полезная.
Why isn’t the verb быть (to be) used in Эта книга полезная?
In Russian, the present-tense copula (equivalent to English is) is usually omitted in simple “X is Y” statements. You wouldn’t say Эта книга есть полезная—you simply say Эта книга полезная.
What gender and case is книга, and why does the adjective end in -ая?
Книга ends in -а, so it’s feminine singular in the nominative case (the “subject” form). Adjectives must agree with their nouns in gender, number, and case. The full form полезная is the feminine singular nominative of полезный (“useful”).
Could we say Эта книга полезна instead of Эта книга полезная?
Yes. полезна is the short-form adjective used predicatively. Both are correct:
- Эта книга полезная (full form)
- Эта книга полезна (short form)
Short forms often sound more formal or emphasize the result/state, while full forms stress the characteristic itself.
Why do we use эта here and not это?