Genitive of negation versus definite accusative

Historically, the Genitive was the strict prescriptive default for negated objects. In modern Russian, the choice reflects semantic nuance. Note that Existential Negation (negating the subject of existence, which is strictly mandatory with words like нет) is distinct from Transitive Negation (negating the direct object of an action, which is variable). For direct objects, the choice is:

• Genitive of Negation (GoN): Used for 'total negation.' It implies the object doesn't exist in the context or refers to a general category.
• Accusative of Negation: Used for 'specific negation.' It implies a particular, pre-identified object exists, but the action simply didn't happen to that one.

Key Factors for Choosing:
1. Verb Aspect: Imperfective verbs favor the Genitive, while Perfective verbs favor the Accusative. However, this is largely a byproduct of specificity. If an object is highly specific, it will remain in the Accusative even with an imperfective verb (e.g., Я не читал эту книгу).
2. Verb Semantics: Verbs of perception, thought, and possession (видеть, знать, иметь) strongly favor the Genitive under negation.
3. The 'Ни' Rule: Double negation with 'ни' (ни одного, никакой) or negative pronouns strongly dictates the Genitive case in standard grammar.
4. Noun Type: Abstract nouns and mass nouns (вода, молоко) strongly default to the Genitive under negation.
5. Animacy and Proper Nouns: Animate nouns and proper nouns generally prefer the Accusative. Because masculine singular and all plural animate nouns have identical Genitive and Accusative forms, the morphological distinction is invisible for them. However, it remains highly visible for feminine singular animate nouns (e.g., не видел маму [Acc] vs. не видел мамы [Gen]), as well as inanimate masculine, neuter, and plural nouns. Verbs of perception or finding can still take the Genitive for proper/animate nouns if the meaning is 'absence from the scene' (e.g., Я не видел вашей сестры - 'I didn't see your sister').
6. Concreteness: Specific items (often with этот or тот) prefer the Accusative.
7. Placement of 'не': For the Genitive of Negation to apply, 'не' must be attached directly to the transitive verb. If 'не' negates another word (like an adverb), the Accusative is required (e.g., Я не вполне понял идею - 'I didn't fully understand the idea' vs. Я не понял идеи - 'I didn't understand the idea').
8. Auxiliary Verbs and Infinitives: When the negated verb is an auxiliary or modal (e.g., хотеть, мочь) and the direct object belongs to a dependent infinitive, the Accusative is generally preferred because the negation is attached to the modal rather than the transitive infinitive, weakening the force of the negation on the direct object (e.g., не хочу читать книгу - 'I don't want to read the book'). However, the Genitive can sometimes still be found (e.g., не хочу терять времени - 'I don't want to lose time'). If separated by two infinitives, the Accusative is strongly preferred (e.g., не хочу начинать писать мемуары - 'I don't want to start writing memoirs'). Furthermore, if the negation is attached directly to the dependent infinitive itself, the Accusative is strongly preferred (e.g., Я прошу не читать эту книгу - 'I ask not to read this book').
9. Word Order (Inversion): Placing the direct object before the negated verb strongly favors the Accusative (e.g., Эту книгу я не читал - 'This book I haven't read').
10. Avoiding Ambiguity: The Accusative is preferred when the Genitive singular form is identical to the Nominative/Accusative plural form to avoid confusion (e.g., Я не читал газету - 'I didn't read the newspaper' over Я не читал газеты - 'I didn't read newspapers').
11. Fixed Expressions: Many idioms permanently freeze the Genitive (e.g., не обращать внимания - 'not pay attention', не играть роли - 'not play a role', не иметь значения - 'not matter', не терять времени - 'not lose time').
12. Register and Style: The Accusative is increasingly the default in colloquial Russian, while the Genitive retains a more formal, literary tone.
13. Prepositional Objects: The Genitive of Negation applies strictly to direct objects without prepositions. Prepositional objects never change their case under negation (e.g., Я не верю в эту идею, never в этой идеи).
14. Other Governed Cases: The Genitive of Negation only applies to direct objects that would normally take the Accusative case. Negation does not alter the case of verbs that inherently govern the Dative, Instrumental, or Genitive (e.g., Я не помогаю маме [Dative]).
15. Double Negation with 'не... не': When a construction uses double negation with 'не' (e.g., не + modal verb + не + infinitive, like не могу не), the negation cancels out to form a strong positive meaning, and the Accusative is strictly required (e.g., Я не мог не прочитать эту книгу - 'I couldn't not read this book').
16. The 'Недо-' Trap: Verbs starting with the prefix 'недо-' (e.g., недооценивать, недопонимать) always take the Accusative because 'не' means 'insufficiently' rather than expressing true negation (e.g., недооценивать проблему, never проблемы).

Additional Notes:

• Subject Genitive of Negation: Beyond direct objects, the Genitive of Negation can also affect the subjects of certain intransitive verbs (verbs of existence, arrival, or appearance) to indicate total absence (e.g., Ответа не пришло - 'No answer came').