быть/стать + Instrumental

This pattern is essential for describing professions, roles, and changing states.

1. The Present Tense:
In the present tense, the verb 'быть' is usually omitted, and the Nominative case is used (e.g., Он — учитель). Even when the present tense form 'есть' is explicitly used, it still takes the Nominative. The Instrumental is triggered by specific grammatical forms of 'быть' (past, future, infinitive, imperative). However, the formal present tense equivalent 'являться' strictly requires the Instrumental case (see Section 4).

2. With the verb 'быть' (to be):
In the past tense, future tense, infinitive, and imperative, the Instrumental is the standard choice for roles and professions. However, in the past tense, bare nouns for professions, nationalities, and social statuses can also take the Nominative to denote a permanent characteristic (e.g., Его отец был адвокат). If the noun is modified by an adjective, the Instrumental case is preferred (e.g., Она была прекрасной актрисой). In modern Russian, the Instrumental case is the standard choice in the future tense (Она будет врачом); using the Nominative in the future (Она будет врач) has a colloquial nuance and is common in relaxed, everyday speech.

• Past: Он был учителем (He was a teacher).
• Future: Она будет врачом (She will be a doctor).
• Infinitive: Я хочу быть врачом (I want to be a doctor).
• Imperative: Будь человеком! (Be a decent person!).

3. With the verb 'стать' (to become):
The verb стать (and its imperfective partner становиться) standardly takes the Instrumental case for nouns because it describes a transition into a new role.

• Он стал инженером (He became an engineer).

Note: For full adjectives, the Instrumental case is the grammatical standard with 'стать' (e.g., 'Он стал старым'), although the Nominative is sometimes heard in casual speech. Short adjectives can also be used with 'стать' (e.g., 'стал известен'), and short adjectives do not decline for case, so they simply take their standard short form.

4. Other common verbs:
Other verbs that describe a state, appearance, or profession also trigger the Instrumental case, such as работать (to work as). Important: While 'работать инженером' is the most standard phrasing, 'работать как инженер' (without a comma) can also mean 'to work as an engineer' (in the capacity of). However, adding a comma ('Он работает, как инженер') creates a comparison meaning 'He works like an engineer'. Other verbs include оставаться / остаться (to remain), казаться (to seem), являться (to be) and служить (to serve as), считаться (to be considered), оказываться / оказаться (to turn out to be), and называться (to be called/named). Note: являться strictly requires the Instrumental case (e.g., 'Он является студентом') and never takes the Nominative. It is primarily restricted to formal, official, or scientific contexts, where it serves as the standard workaround to express 'is + [Instrumental]' in the present tense. Also, be careful with кажется: when used as a verb, it takes the Instrumental (Это кажется ошибкой), but when used as a parenthetical word meaning 'it seems', it does not affect the case (Это, кажется, ошибка).

• Она работает врачом (She works as a doctor).
• Мы остались друзьями (We remained friends).
• Это кажется ошибкой (This seems like a mistake).
• Он является директором (He is the director).
• Это служит примером (This serves as an example).
• Он считается экспертом (He is considered an expert).
• Это оказалось правдой (It turned out to be the truth).
• Этот город назывался Ленинградом (This city was called Leningrad).

5. Verbs of motion and position:
Verbs of motion (вернуться, приехать, уйти) and position (сидеть, стоять, лежать) can also take the Instrumental case when describing the state of the subject during the action.

• Он вернулся усталым (He returned tired).
• Она сидела грустной (She sat sad).

6. Adjective Agreement:
If you use an adjective to modify the predicate noun, it must agree with that noun and also take the Instrumental case.

• Он был хорошим студентом (He was a good student).

7. Semantic Note:
There is an important distinction in modern Russian: the Nominative is usually the standard choice for permanent, inherent qualities (e.g., Она была красавица), while the Instrumental tends to be used for temporary roles or acquired statuses (Он был директором). This same logic applies when an adjective stands alone as the predicate (e.g., 'Он был молодой' for a permanent characteristic vs. 'Он был молодым' for a temporary state in the past).

8. Short Adjectives:
A core rule of Russian predicate grammar is that short adjectives never take the Instrumental case. Short adjectives do not decline for case, so they simply take their standard short form regardless of the tense of 'быть' (e.g., it is always 'Он был болен' or 'Она будет готова', never 'больным' or 'готовой').

9. Pronouns:
Personal pronouns usually stay in the Nominative case in the predicate (e.g., 'Это был он'). This is a helpful exception for learners.

10. The 'Это' Construction:
When the subject is the demonstrative pronoun 'это', the predicate noun typically remains in the Nominative case even in the past and future tenses.

• Это была ошибка (It was a mistake).

11. Inanimate Objects:
When simply identifying inanimate objects in the past or future, the Nominative case is used (e.g., Там был стол, never 'Там было столом').