Zero copula in academic definitions

In Russian, the present tense of the verb 'to be' (быть) is almost always omitted. This is known as the zero copula. In standard written Russian, this omission is orthographically marked with a dash (тире) under specific conditions.

1. Morphological Requirements:
To show identity or provide a definition, the zero copula requires both the subject and predicate to be in the nominative case. Unlike the past or future, which often require the instrumental, both the subject and the predicate remain in the nominative.

2. Mandatory Dash Contexts:
The dash is required in standard written Russian between:

• Noun — Noun: Москва — столица России. (Moscow is the capital of Russia.)
• Noun — Infinitive: Наша цель — победить. (Our goal is to win.)
• Infinitive — Infinitive: Жить — Родине служить. (To live is to serve the Motherland.)
• Numeral — Numeral: Дважды два — четыре. (Two times two is four.)

3. Conditional Dash Contexts:
A dash between an infinitive subject and an adverbial predicate (Category of State) is conditional and depends on an intonational pause (e.g., Курить — вредно. - Smoking is harmful.).

4. Omission of the Dash:
The dash is typically omitted in the following cases, though it can still be used for logical emphasis, intonational pauses, or structural parallelism (e.g., Ночь — тёплая, небо — синее. - The night is warm, the sky is blue.):

• Conversational Style: In informal speech and writing, the dash is often dropped (e.g., Мой брат инженер. - My brother is an engineer.).
• Inverted Word Order: When the predicate precedes the subject (e.g., Прекрасный человек Иван Иванович! - Ivan Ivanovich is a wonderful person!).
• Adjective Predicates: If the predicate is an adjective (e.g., Этот город красивый. - This city is beautiful.).
• Personal Pronouns: When the subject is a pronoun (e.g., Я врач. - I am a doctor.), unless emphasized for contrast.
• Negative Particle: When не is present before a noun predicate (e.g., Бедность не порок. - Poverty is no vice.). However, the dash is usually retained if the predicate is an infinitive (e.g., Жизнь прожить — не поле перейти. - Living a life is not like crossing a field.).
• Introductory Words/Particles: The dash is omitted if words like ведь, тоже, также, конечно, or просто stand between the subject and predicate (e.g., Мой брат тоже инженер. - My brother is also an engineer.).
• Comparative Conjunctions: Before как, словно, or будто (e.g., Пруд как зеркало. - The pond is like a mirror.).

5. Use with 'Это', 'Вот', and 'Значит':
When это, вот, or значит is used to link the subject and predicate, the dash is placed before these words (e.g., Геометрия — это наука. - Geometry is a science., Понять — значит простить. - To understand means to forgive.). Note the critical difference between 'это' as a copular particle (dash used: Книга — это друг. - A book is a friend.) and 'это' as a demonstrative pronoun subject (no dash: Это моя книга. - This is my book.).