Why do stress patterns often match between cognates in Russian and Ukrainian?

Question

I sometimes find myself looking up Russian words on wiktionary and following the etymology of the word upstream to find what words it is related to, as you do. I think I've noticed a peculiar thing: in words of the same origin, the Eastern Slavic languages seem to agree pretty well on which one of the syllables is stressed. For example, the corresponding forms of górod are in Belorussian stressed as "hórad", and in Ukrainian, "hórod". There's also "molokó" vs "malakó", etc. It doesn't seem to hold true outside of the Eastern branch, as the Polish form of "zemljá", "zemia", is stressed on the first syllable.

What is the cause of this pattern? Is this an Eastern Slavic thing which they inherited from their most recent common ancestor, did they borrow it from Church Slavonic, or is it simply that Belorussian and Ukrainian have for most of their recent history been treated as Russian dialects and come under heavy Russian influence?

To speakers of the other Eastern Slavic languages, what are some exceptions to the rule?

Answer 1

Your claim is just wrong. While Russian and Ukrainian are very closely related indeed (so this is an answer to your question - why the majority of words that share same origin share same stress pattern as well), there are like a lot of words where the Ukrainian stress is counter-intuitive to a Russian monolingual speaker. In fact, if you'll give a Ukrainian text to Russian speaker he will certainly do noticeable amount of errors with stressing.

I'm a Russian speaker who happened to visit Ukraine quite often and one of the hardest thing in Ukrainian is exactly not to make errors of this kind.

Off the top of my head:

• "были" - "були"
• "жизнь" - "життя"
• "волосы" - "волосся"
• "козлёнок" - "козеня"
• "помер" - "помер"

UPD: my understanding of cognates (quite possibly was wrong)it's they are ethymologycally stem from one root, but ok, let me add some stricter examples:

• "говоришь" - "говориш"
• "страшный" - "страшний"
• "редкий" - "рiдкий"
• "хочу" - "хочу"
• "другой" - "другий"
• "мышиный" - "мишачий"
• "белизна" - "білизна"
• "начинка" - "начинка"
• "распродажа" - "розпродаж"

Answer 2

The history of the modern Russian language is remarkable in that it appeared from convergence of two distinct dialects in about equal parts (Nothern and South-Eastern; only the latter you might call 'the speech of Kievan Rus'). The 'Northern' (or Novgorod/Pskov) dialect predates the Ukranian/Russian/etc. languages per se; it stands in equal opposition to other Slavic groups including the Western one.

More info if you read in Russian (esp. second half).

As a result, in some cases you find a perfect match with the south/eastern Slavic languages, while in others there is something different. This concerns not just the stress, but primarily grammatical and phonetical rules, of which stress is just a small part.

As an example, I'll quote a small part from Zalisnyak I linked above:

...на северо-западе говорили на руке, в то время как на востоке было на руце. Сейчас мы говорим целый, но на руке. Это не что иное, как соединение того целый, которое идет с востока, с тем на руке, которое идет с северо-запада.

(You'll find "на руци" (руці etc.) in most other Slavic languages, including Ukrainian, Serbian or Czech).

With respect to stress, the Western Slavic languages underwent a more rapid change towards a more consistent stress pattern. Czech finished with all stress on the first syllable. Polish is a bit more difficult but is still way more consistent than Russian. Russian is still on its way, but linguists say a pattern is likely to emerge eventually. Which one we don't know yet. But perhaps partly due to its unique ancestry it may take longer.