GrammatikNomen Belebtheit

Russian nouns are classified as animate (alive) or inanimate (not alive). This is called "aliveness" or "animacy" and mainly affects grammar in the Accusative case.

What counts as animate?

Animate (одушевлённые):

• Humans: человек, студент, мама
• Animals: собака, кот, птица
• Sometimes fictional beings: робот, призрак

Inanimate (неодушевлённые):

• Objects: стол, книга, телефон
• Abstract concepts: идея, любовь
• Plants are usually treated as inanimate: дерево, цветок

Why it matters (Accusative case)

Knowing the aliveness is important for the declension of nouns and adjectives. You always need it when declining a male noun or a plural form. In all following examples we will use sentences with verbs that require the Accusative case.

Accusative Singular (for masculine Nouns)

For masculine (singular), the Accusative will be the same as either Nominative or Genitive, depending on the aliveness.

• Inanimate → Nominative
  Я вижу стол. (I see the table.) → This Accusative is the same as the Nominative.
• Animate → Genitive
  Я вижу брата. (I see the brother.) → This Accusative is the same as the Genitive.

Here on OpenRussian you can also see it in the declension tables.

• For inanimate nouns, the Accusative is always the same as the Nominative, for example in год (year), глаз (eye), ве́чер (evening).
• For animate nouns, the Accusative is always the same as the Genitive, for example in сын (son) or инженер (engineer) or пилот (pilot).

Feminine nouns

Just for comparison, here is how for female nouns nothing changes:

• Я вижу сестру (animate), Я вижу книгу (inanimate) → no visible difference.

Accusative Plural (all gender nouns)

For Plural (all genders) there is an equivalent rule for Accusative:

• Inanimate → Nominative Plural
  Я вижу столы. (I see the tables.) → This Accusative Plural is the same as the Nominative Plural.
• Animate → Genitive Plural
  Я вижу же́нщин. (I see the women.) → This Accusative Plural is the same as the Genitive Plural.

Accusative for Adjectives

For Adjectives, the same rule applies: In Accusative they follow the noun and change depending on animacy, for male nouns and all plurals.

• Masculine (singular)
  Inanimate → Nominative form
  Я вижу новый стол. (I see a new table.)
  Animate → Genitive form
  Я вижу нового студента. (I see a new student.)
• Plural (all genders)
  Inanimate → Nominative Plural
  Я вижу новые столы. (I see new tables.)
  Animate → Genitive Plural
  Я вижу новых студентов. (I see new students.)
• Feminine (singular) no change
  The form is fixed, so animacy does not change it:
  Я вижу новую сестру. (I see a new sister.)
  Я вижу новую книгу. (I see a new book.)

In short: adjectives always agree with the noun, so whenever animacy affects the noun, it also affects the adjective.

Some exceptions

• Words like труп (corpse) → grammatically animate.
• Words like народ (people as a group) → inanimate.
• Some creatures or characters depend on meaning/context.

Summary

• If it is a person or animal it's animate/alive, else inanimate/not alive.
• Sets Accusative form for male nouns and plurals: Nominative for inanimate and Genitive for animate.