Это заболевание опасное.

This disease is dangerous.

Breakdown of Это заболевание опасное.

• это: this
• опасный: dangerous
• заболевание: the disease

Questions & Answers about Это заболевание опасное.

Why is there no verb to be in Это заболевание опасное?

In modern Russian the present-tense form of the verb быть (“to be”) is typically omitted. You simply state the subject and its quality. In past or future you would use было or будет, but in the present tense you say Это заболевание опасное and the meaning “This disease is dangerous” is understood.

What part of speech is это here, and why can’t I use этот instead?

Here это is a demonstrative pronoun meaning “this.” It agrees with a neuter noun in the nominative singular. заболевание is neuter, so you use это заболевание. этот is the masculine form; the full demonstrative-adjective paradigm is этот (masc.), эта (fem.), это (neut.), эти (plur.).

Why does опасное come after the noun instead of before it?

When an adjective functions as part of the predicate (“is dangerous”), it commonly follows the noun in Russian: заболевание опасное. If you place the adjective before the noun (опасное заболевание), it works attributively (“a dangerous disease”), not as the predicate of a clause. Both are grammatically correct, but the first is more like “This disease is dangerous,” while the second is “this dangerous disease.”

Why does опасное end with -ое? What does that ending tell us?

Russian adjectives must agree with the noun they describe in gender, number, and case. заболевание is neuter, singular, nominative, so the adjective takes the neuter singular nominative ending -ое. If the noun were masculine it would be опасный, feminine опасная, and plural опасные.

Can I use the short-form adjective опасно instead of the long form опасное?

Yes. The short-form neuter опасно also works as a predicate: Это заболевание опасно. Short forms are often more neutral or colloquial when stating a condition, whereas the long form (here опасное) can sound slightly more descriptive or formal, but both are correct.

How do I turn Это заболевание опасное into a question (“Is this disease dangerous?”)?

You have two common options:
1) Simply raise your intonation at the end: Это заболевание опасное?
2) Use the question particle ли and invert word order: Опасно ли это заболевание?

How do I make that sentence negative (“This disease is not dangerous”)?

Place не before the adjective (long or short):

• With long form predicate: Это заболевание не опасное.
• With short form: Это заболевание не опасно.
  If you prefer the attributive structure, you can also say Это не опасное заболевание.

How would I say “This disease is very dangerous” in Russian?

Insert the intensifier очень before the adjective:

• Predicatively: Это заболевание очень опасное.
• Attributively: Это очень опасное заболевание.