быть / стать / работать + Instrumental

The Predicative Instrumental is used to identify a subject's role, status, or perceived state. It is the standard way to discuss careers and life changes.

1. Trigger Verbs:

• быть (to be): Used in the past (был/была/было/были) and future (буду/будешь...). Note: The present tense 'есть' is usually omitted and the noun stays in the Nominative.
• стать (to become): Requires the Instrumental for nouns. For adjectives, the Nominative is widely accepted and grammatically correct, especially in spoken Russian or for stylistic emphasis (e.g., Она стала красивая).
• работать (to work as): Used to describe one's employment.
• остаться / оставаться (to remain/stay): Used to describe a continuing state or role.
• называться (to be called): Used for names or titles of things. Note: When giving the actual proper name or title, the Nominative is the standard, often in quotes (e.g., Книга называется «Война и мир»).
• являться (to be/serve as): A formal equivalent of 'to be'. Unlike 'быть', it is actively used in the present tense and always requires the Instrumental (e.g., Он является директором).
• казаться (to seem): Used to describe how something appears.
• оказаться (to turn out to be): Used to describe a discovered state or role.
• считаться (to be considered): Used to describe how someone or something is viewed.

2. Nuance:
When using быть in the past tense, the Instrumental implies a temporary, acquired, or changeable state (e.g., Он был студентом), while the Nominative implies a permanent or inherent characteristic (e.g., Он был слепой). For nouns, the Instrumental is the standard for written and formal contexts when using 'быть' in the past or future tense to denote a role or status. The Nominative is largely restricted to colloquial speech, simple identification, or expressive/evaluative nouns (e.g., Они были молодцы).

3. Morphology (Singular Endings):

• Masculine/Neuter Nouns: -ом (hard), -ем (soft). Example: студент → студентом.
• Feminine Nouns: -ой (hard), -ей (soft), -ью (soft sign). Examples: актриса → актрисой, вещь → вещью. Nouns ending in -ия change to -ией (e.g., профессия → профессией). Note the irregular forms: мать → матерью, дочь → дочерью.
• Spelling Rule for Hushers (ж, ш, ч, щ) and ц: After these consonants, the choice between -ом/-ой and -ем/-ей is dictated by stress. Stressed endings take -ом/-ой (врач → врачом), and unstressed endings take -ем/-ей (муж → мужем).
• Adjectives: Masculine/Neuter: -ым/-им. Feminine: -ой/-ей.

4. Morphology (Plural Endings):

• Nouns (All Genders): -ами (hard), -ями (soft). Example: врачи → врачами, учителя → учителями.
• Irregular Plurals: The highly common words 'люди' (people) and 'дети' (children) have irregular Instrumental plural forms: людьми and детьми.
• Adjectives: -ыми/-ими.

5. Personal Pronouns in the Instrumental:
мной (me), тобой (you, informal), им (him/it), ей (her), нами (us), вами (you, formal/plural), ими (them).

6. Adjective Agreement:
If you include a full adjective, it must also be in the Instrumental case (e.g., хорошим врачом). Note: Short-form adjectives (e.g., рад, готов, болен) never take the Instrumental case; they always remain in the Nominative, even with 'быть' in the past or future.