Эта книга тонкая, но очень интересная.

the book

Breakdown of Эта книга тонкая, но очень интересная.

• интересный: interesting
• но: but
• очень: very

Questions & Answers about Эта книга тонкая, но очень интересная.

Why is it эта книга and not этот книга?

Because книга is a feminine singular noun, and эта is the feminine singular form of этот (this).

Russian demonstratives must agree with the noun in:

• gender
• number
• case

So:

• этот = masculine
• эта = feminine
• это = neuter
• эти = plural

Since книга is feminine, you say эта книга = this book.

How do I know that книга is feminine?

In Russian, many nouns ending in -а or -я are feminine, and книга follows that pattern.

So learners often recognize:

• книга → feminine
• машина → feminine
• неделя → feminine

Because книга is feminine, any adjectives or words like this that go with it must also be feminine:

• эта книга
• тонкая книга
• интересная книга

Why do both adjectives end in -ая: and ?