Ordinal Numbers

Ordinal numbers answer "which one in the sequence?" — first, second, third — as opposed to the cardinals (one, two, three) that answer "how many?". The single most useful thing to know about them is also the easiest: in Russian, ordinals are adjectives, plain and simple. They are not a special part of speech with their own quirky government like the cardinals. They decline and agree in gender, number, and case exactly like any other adjective — пе́рвый день, пе́рвая кни́га, пе́рвое сло́во, на пе́рвом этаже́. If you can handle но́вый ("new"), you can handle пе́рвый. There is only one truly irregular form (тре́тий) and one rule that surprises everyone (compound ordinals decline only their last word). Beyond that, ordinals are the calm corner of the number system.

The basic ordinals

Note the stress shifts and the two that are built on different roots (второ́й, not два-related; сороково́й). *Тре́тий is the lone irregular: it is a soft adjective with a fleeting -и- and unusual short endings.

Ordinals decline and agree like adjectives

Because ordinals are adjectives, they take the full adjectival paradigm and must match their noun in gender, number, and case. There is nothing numeral-specific to memorise here — it is the regular hard-adjective declension (and for тре́тий, the soft one).

The irregular тре́тий

Тре́тий is soft throughout and inserts a soft sign before its endings: тре́тья (fem.), тре́тье (neut.), тре́тьего (gen.), тре́тьему (dat.), тре́тьем (prep.). Treat it as a one-off and learn it by ear.

Compound ordinals: only the LAST word is ordinal

Here is the rule that catches every learner, because it is the exact opposite of how cardinals behave. In a compound cardinal, every word declines (с двадцатью́ пятью́). In a compound ordinal, only the final word becomes the ordinal and declines; every word before it stays a plain cardinal in the nominative.

So "the twenty-first" is два́дцать пе́рвый — два́дцать is the bare cardinal, only пе́рвый is the ordinal. The huge year-numbers work the same way:

Where ordinals do their everyday work

Dates

The day of the month is an ordinal. Naming a date uses the nominative (agreeing with the implied neuter число́, "date"); saying an event happens on a date switches to the genitive. Full detail on the genitive in dates and time.

Floors and clock-time

Floors take the prepositional with на (на тре́тьем этаже́). For the approximate hour, Russian has the idiom в + prepositional of the ordinal + часу́ — "in the Nth hour", i.e. between (N−1) and N o'clock: в пе́рвом часу́ means "some time after twelve, before one".

How this differs from English

English ordinals are tiny invariable tags glued to the number ("the twenty-first", "1984") and never change shape. Russian ordinals are full adjectives that must agree and decline — so "the twenty-first" becomes два́дцать пе́рвый / пе́рвая / пе́рвое / пе́рвого depending on what it modifies and the case it sits in. The compound rule also flips English intuition: English happens to inflect only the last element too ("twenty-first", not "twentieth-first"), so that part feels familiar — but English does this by leaving the ordinal form on the last word, whereas Russian leaves the earlier words as undeclined cardinals and only the last word takes the adjective endings. The real workload for an English speaker is remembering to decline the ordinal at all, since English never does.

Common Mistakes

Key Takeaways

• Ordinals are adjectives: they decline and agree in gender, number, and case (пе́рвый день, пе́рвая кни́га, на пе́рвом этаже́). No special numeral government.
• Most are regular hard adjectives; тре́тий is the one irregular, soft form (тре́тья, тре́тье, тре́тьего, тре́тьем).
• In a compound ordinal only the last word is ordinal and declines; everything before it stays a bare cardinal (два́дцать пе́рвый; ты́сяча девятьсо́т во́семьдесят четвёртый). This is the mirror image of the cardinal rule.
• Ordinals run dates (пе́рвое ма́я nom. / пе́рвого ма́я gen.), floors (на тре́тьем этаже́), and the approximate hour (в пе́рвом часу́).