In short

The instrumental (ору́дний відмі́нок) is the case of the tool you act with and the thing you become or are called. Its two everyday jobs map onto two English words:

• by / with (a means) — write with a pencil, travel by train: no preposition, just the ending. Its question is чим? “with what” (or ким? “by/with whom”).
• be / become something — after an overt бути (“be”) in the past or future, and after ста́ти (“become”) or працюва́ти (“work as”), the predicate noun takes the instrumental: Він був студе́нтом “He was a student.”

Watch one spelling twist: soft feminine nouns like сіль, ніч, тінь double their last consonant before the ending — сі́ллю, ні́ччю, ті́нню.

The rule

1. Means and instrument — bare instrumental. The thing you use to do something goes straight into the instrumental, with no preposition: писа́ти олівце́м (write with a pencil), рі́зати ноже́м (cut with a knife), ї́хати по́їздом (go by train).

2. “With” as company — з + instrumental. English “with” also means “in the company of”. For that, Ukrainian uses the preposition з: з дру́гом (with a friend), з ча́єм (with tea). So писа́ти олівце́м (tool, no з) but гуля́ти з дру́гом (company, з). Do not put з in front of a tool.

3. Predicate instrumental — бути + орудний. When you say “X is/was/will be a Y”, the role noun Y takes the instrumental — but only once the verb «бути» is spoken:

• Present, zero copula → nominative: Він лі́кар. “He is a doctor.”
• Past / future бути → instrumental: Він був лі́карем. Він бу́де лі́карем.
• Become / work → instrumental: Вона́ ста́ла лі́карем. Вона́ працю́є лі́карем.

The same holds after здава́тися (seem), вважа́тися (be considered), назива́тися (be called).

4. Prepositions that govern the instrumental. над (above), пе́ред (before, in front of) and між (between) always take this case. з takes it in its “with, together with” sense (з дру́гом) — з meaning “from, out of” takes the genitive instead (з кімна́ти, see lesson 9). під (under) and за (behind) take the instrumental for a static position (де? — під столо́м, за буди́нком) but the accusative for motion towards (куди? — під стіл, за буди́нок, see lesson 23). Also a few verbs: пиша́тися (be proud of), ціка́витися (be interested in), займа́тися (be occupied with), керува́ти (manage, drive).

5. Time. Parts of the day and seasons stand in the bare instrumental to mean “during”: ні́ччю (at night), ра́нком (in the morning), ве́чором (in the evening), весно́ю (in spring).

6. The doubling behind сі́ллю / ні́ччю / ті́нню. Third-declension feminine nouns (soft, ending in a consonant) add -ю, and a single soft or hushing consonant caught between two vowels is lengthened, written as a doubled letter: сіль → сі́ллю, ніч → ні́ччю, тінь → ті́нню, по́дорож → по́дорожжю. This is the very same sound-lengthening that is frozen into a set of neuter -я nouns — знання́ (knowledge), життя́ (life), обли́ччя (face) — where the double letter is simply part of the word. Seeing the doubling there is the передумо́ва, the precondition, for spelling it here: it is one phonetic rule, once lexical, once grammatical.

Two brakes on that doubling: after a labial (б, п, в, м, ф) there is no double letter — write an apostrophe instead: любо́в’ю, кро́в’ю; and after a consonant cluster the consonant does not double: ра́дість → ра́дістю.

Forms & patterns

Endings by gender and hard/soft stem (singular):

Third-declension feminine — the consonant-doubling group in focus:

Plural (all genders): -ами / -ями, with a few irregulars in -ми.

Personal pronouns:

Examples

Common mistakes

• писа́ти з олівце́м -> писа́ти олівце́м — a tool takes the bare instrumental; з is only for company, not for means.
• Він був учи́тель -> Він був учи́телем — after an overt бути (past/future) the predicate role noun goes to the instrumental, not the nominative.
• Він є лі́карем (about the plain present) -> Він лі́кар — in the present with zero copula the predicate is nominative; the instrumental appears only when бути / ста́ти / працюва́ти is spoken.
• сі́лю / ніч’ю / тінью -> сі́ллю / ні́ччю / ті́нню — a single soft consonant doubles before -ю; no apostrophe, no single letter.
• любо́вю / кро́вю -> любо́в’ю / кро́в’ю — after a labial (б, п, в, м, ф) there is no doubling; you write an apostrophe instead.
• ра́діттю -> ра́дістю — no doubling when the stem already ends in a consonant cluster (-ст-).
• знаням / житям (single н, single т) -> знання́м / життя́м — these neuter nouns carry a doubled letter in the stem; keep both letters in the instrumental.

Tips

• Ask чим? “with what” (things) or ким? “with/by whom” (people) to locate an instrumental in a sentence.
• No preposition for a means (олівце́м, по́їздом); reserve з for accompaniment (з дру́гом, з ча́єм).
• Reach for the predicate instrumental the moment бути is voiced: був / бу́де / ста́ти / працюва́ти + -ом / -ем / -ою / -ею.
• Memorise the instrumental prepositions in two groups: над, пе́ред, між always take it, while з, під, за take it only in the readings above (з = “with”, під/за = a static position).
• For сіль-type nouns, say the ending aloud: a lengthened consonant + ю — сі́л-л-ю, ні́ч-ч-ю, ті́н-н-ю. The doubled letter just writes that length down.
• Let the neuter nouns знання́, життя́, обли́ччя remind you what the doubling sounds like before you apply it to сі́ллю, ні́ччю, ті́нню.
• Mind mobile stress: it often jumps onto the ending — стіл → столо́м, ніж → ноже́м, вода́ → водо́ю.