Typically, when forming the genitive plural of some word which in the nominative ends in -CCа (where C represents a consonant, such that this represents a consonant cluster followed by "а") the ending vowel is removed and an insert vowel like е, ё, or о is inserted. Consider:

ошибка --> ошибок; письмо --> писем ...etc.

My question regards the formation of the genitive plural of words ending in -CьCа like просьба and свадьба. Whereas the genitive plural of свадьба is сва́деб, the genitive plural of просьба is просьб. Is this simply a result of some historical linguistic development? Or is there some other reason for why the genitive plural of просьба is not просеб?

  • i think that previous posts are more than correct, and I think, that there is no strong rule for all cases, there is many exeptions beside the rule and there is soft sign ' ь ' before hard sound ' b ' so it's ends hard way too.
    – user6861
    Commented Feb 28, 2016 at 21:14

3 Answers 3


I've checked words ending with all (or almost all) possible combinations of C1C2V and C1ьC2V type, where C1 and C2 are different consonants, and V is vowel а, я, о or е. The main conclusions are:

  1. Most of the combinations don't follow the question author's rule.
  2. But some of them do, and in most of them C2 is к, л, н or ц.
  3. Some combinations with C2 = б, г, м or р follow the rule, too, but they are much less numerous.
  4. For the rest values of C2 I didn't find a single word following the rule.

Here are the combinations following the rule:

C2 = к

C1 can be any other consonant. No exceptions found (for some rare combinations, like гка or щька no proofs found, as well, but if such words exist, they should follow the rule, too).

C2 = н

  1. C1 = б, в, г, ж, к, м, п, с, т, х, ч, ш. These combinations follow the rule, no exceptions found.
  2. C1 = д, з, л. Only words with palatalized C2 follow the rule (обедня - обеден, кузня - кузен, мыльня - мылен, but ехидна - ехидн, тризна - тризн, волна - волн).
  3. For C1 = ф, ц and щ no examples found.

C2 = л

This case is very irregular. Some combinations follow the rule, some don't, and the majority of them follows it partly. I think, no rules can be successfully applied here, the best way to deal with it is to learn as many words as possible, so that you just remember the most common ones and develop some intuition for the rest.

C2 = ц

I've found examples only for C1 = в, д, л, н, р, т. All of them follow the rule, except for one word: солнце - солнц. For other values of C1 I didn't find any words, but my intuition says that if there are, most of them should follow the rule, too.

Other combinations, which follow the rule: дьб, ньг, рьг, "др" followed by "о".

Words following the rule while the corresponding combination doesn't follow it in general: розга - розог, тюрьма - тюрем, письмо - писем, ребро - рёбер.

I still don't understand, why the situation is as described above, and not some other way. If anyone has any suggestions, please write them in comments! Thanks!

  • Thank you for the response! This is very interesting to me, as an American student learning Russian. In all the textbooks I've had, I've been taught to break up word ending consonant clusters with insert vowels in the genitive plural. Your response certainly complicates the textbook's picture. Commented Mar 4, 2016 at 5:26
  • 1
    Such generalization in the textbooks looks surprising, but is reasonable to some extent, because frequency of combinations is dramatically different. There are thousands of words ending with -ка, and new ones can be created instantly from almost anything. For example, SMS if often called "эсэмэска", Windows XP can be called "экспишка", and my former boss called backend servers in Perl programming language "перлячка"... and so on. These words sound quite natural, follow normal rules of Russian language, and I think nearly any native speaker has invented something like this at least once.
    – Lara
    Commented Mar 4, 2016 at 14:25
  • Other popular endings are "-ко", "-ня", "-це", words with them tend to follow the rule. But for the majority of consonants combinations there are less than 5 words, or no words at all. So, if we count words, not combinations, then we will really see, that the majority of words follows the rule. Just because words ending with "-ка" overwhelm everything else. That's why, that simplification in textbooks is understandable, even though there are tons of exceptions, because for most words it works! :)
    – Lara
    Commented Mar 4, 2016 at 14:34

Not sure but I think that's because "просьба" is pronounced as "прозьба" ("с" becomes voiced because the following "б" is paired voiced). So if it were "просеб", "с" wouldn't become voiced unlike its actual pronunciation... maybe that's why for some historical reasons "просьб" has no vowel between "с" and "б" in this form.

And I can not coin another example with the equivalent feature :)

  • 2
    I've found one more example: ведьма -> ведьм, not "ведем". But I've no idea why...
    – Lara
    Commented Feb 26, 2016 at 13:52
  • 2
    And one more: резьба - резьб. Also some combinations of consonants without "ь" don't follow this rule. For example, "зм" (призма - призм, клизма - клизм), "чт" (мачта - мачт, почта - почт), "чв" (почва - почв). Probably, "сьб" (and "зьб") just don't follow it, too. But I still don't know, why.
    – Lara
    Commented Feb 26, 2016 at 14:06
  • @Lara u coined co many examples, are you native? :) and if not, what's your native language? Commented Feb 26, 2016 at 17:41
  • yes, I'm native Russian, but I think this is off-topic here :)
    – Lara
    Commented Feb 28, 2016 at 14:59
  • @Lara yup, but as long as I don't know how to find u in social networks I have no other way to get acquainted :) Commented Mar 8, 2016 at 0:27

I think свадеб is the real outlier here. Просьб is in line with служб, тяжб, and even женитьб. What's more, I think свадеб is a later development, driven by ease of pronunciation, from an earlier *свадьб. Had the vowel been around since the schwa extinction (as in ошибок and писем), it would have been the etymologically correct *сватеб.

  • 1
    But "судьба" - "судеб" and "усадьба" - "усадеб". So, words with "дьб" tend to follow the rule suggested in the question. Are there any words of this type with equal consonants, but different behaviour in genitive plural?
    – Lara
    Commented Feb 28, 2016 at 14:55
  • @Lara Oh. I missed these. And I don't think there are ones that behave differently. Does молотьба have a gen. pl. at all? Wiktionary lists "моло́тьб" with an asterisk in front. Commented Feb 28, 2016 at 16:29

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