Today the following sentence came up in a chat with a Russian friend:

Ты был забавным.

Here the adjective is in dative instrumental case, but I would expect it to be in nominative together with the verb был/быть.

When I asked my friend why she didn't write Ты был забавный, she explained that this was because it was in past tense. But I cannot find this rule anywhere in Russian grammar books.

Can anybody explain the use of dative instumental in this sentence?

Edit: I mistakenly wrote dative case above. I meant instrumental case.


2 Answers 2


The noun and adjective functioning as the nominal part of a compound predicate can be in the nominative or in the instrumental case. Typically, the nominative here [where the linking verb быть is present] corresponds to a permanent quality of the subject while the instrumental case better combines with a temporary quality.

In much more detail (Розенталь Д.Э., Джанджакова Е.В., Кабанова Н.П.CПРАВОЧНИК ПО ПРАВОПИСАНИЮ, ПРОИЗНОШЕНИЮ, ЛИТЕРАТУРНОМУ РЕДАКТИРОВАНИЮ, M.: ЧеРо, 1999): http://www.evartist.narod.ru/text1/62.htm#%D0%B7_02

(see §179. Формы сказуемого)


What can be added to the answers in the past topics referenced by Sergey Slepov in the comments, is that at least in your example, usage of adjective in nominal or instrumental affects semantics of the phrase.

Ты был забавный Nom. would relegate your being забавный to a distant past, when there was another you so to speak, for example in the childhood, youth etc, that is once you were so. That's probably agrees with the fact of it indicating permanent (or stable within certain time limits) quality as mentioned elsewhere.

Ты был забавным Instr. can be applied to any time span.

  • Thank you for your answer and reference to the previous topic on essive. Yes, this is instrumental case, I was mistaken when I wrote dative case originally.
    – joshualotz
    Commented May 11, 2018 at 20:16
  • @joshualotz sure, no prob, mistakes are welcome Commented May 11, 2018 at 20:53
  • 1
    @joshualotz I too was very surprised when I first met this construction since it was not taught in any course or textbook I had as a student. It applies to the future tense as much as the past (just not the present), e.g., когда я был студентом... and когда я буду аспирантом...
    – KCd
    Commented May 12, 2018 at 1:52

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