Collective numerals

Collective numerals are a unique feature of Russian grammar used in specific contexts:

1. Usage Constraints:

• Masculine or Mixed-Gender Groups: двое студентов (two students, at least one is male). For groups of only females, standard cardinal numbers are used in standard or formal Russian, with the exception of the collective numeral обе (both - feminine). Note that in colloquial speech, collective numerals are sometimes used with females (e.g., пятеро дочерей).
• Masculine Nouns Ending in -а/-я: Collective numerals are highly preferred with masculine nouns ending in а or я (e.g., двое мужчин, трое юношей).
• Specific Human Nouns: Collective numerals are standard and highly preferred with words like ребята (guys/kids) and лица (persons/individuals) (e.g., трое ребят, четверо незнакомых лиц). Note on "people": The standard way to count people is using cardinal numerals with человек (e.g., два человека). Collective numerals with люди are typically only used when accompanied by an adjective (e.g., трое молодых людей).
• Children and Young Animals: трое детей (three children), четверо котят (four kittens). Standard cardinal numbers must be used for adult animals (e.g., три кота).
• Plural-only Nouns (Pluralia Tantum): For nouns like сутки (24-hour period) or ножницы (scissors), collectives are mandatory for numbers 2–4 in the Nominative and Inanimate Accusative cases. For numbers 5 and above, standard cardinal numbers are more common because the conflict disappears at 5, as cardinal numbers 5 and above naturally govern the Genitive Plural (e.g., пять суток). Note: оба/обе cannot be used with pluralia tantum nouns.
• Paired Items: Collective numerals are used with nouns denoting paired items to mean 'pairs of' (e.g., двое носков = two pairs of socks, трое сапог = three pairs of boots).
• Standard Inanimate Nouns: Collective numerals (except оба/обе) cannot be used with standard inanimate nouns. For example, двое столов is strictly incorrect; you must use два стола.
• Substantivized Adjectives and Participles: Collective numerals are highly preferred or mandatory with adjectives and participles acting as nouns that denote people (e.g., двое прохожих, трое больных).
• Personal Pronouns: нас было пятеро (there were five of us).
• Compound Numerals: Collective numerals cannot be part of compound numerals (e.g., двадцать два студента is correct, not двадцать двое студентов). For pluralia tantum nouns in compound numbers, you must rephrase (e.g., use двадцать два дня instead of trying to combine 22 with сутки).
• Stylistic Constraints: Collective numerals are generally avoided with high-status nouns or official ranks in formal speech (e.g., use два профессора instead of двое профессоров).

2. Grammatical Cases:

• In the Nominative (and Inanimate Accusative), numerals like двое-десятеро govern the Genitive Plural of the noun, while оба/обе govern the Genitive Singular (e.g., обе студентки).
• In Oblique Cases (Genitive, Dative, etc.), the numeral behaves like a plural adjective and must agree with the noun in case. Note: оба/обе agree with both animate and inanimate nouns in oblique cases. However, двое-десятеро are strictly replaced by cardinal numbers for inanimate nouns in oblique cases (e.g., около трёх суток, not троих).
• For Animate Nouns, the Accusative case of the collective numeral is identical to its Genitive form (e.g., я видел двоих друзей).

3. Range: Only numbers 2 through 7 are commonly used. Beyond 7, standard cardinal numbers are preferred.