Genitive Ending for Second Declension Singular Masculine Inanimate Nouns

Question

My grammar table lists two sets of endings, one of which is equivalent to those for animate nouns and the other, which is:

consonant: +а
ь, й→я

How do I know which to use?

Answer 1

If fact, there is no concrete-and-simple rule that would say, whether -а/-я or -у/-ю should be used for genitive singular of a specific second-declension noun — people generally just intuitively remember endings.

The very imprecise rule is that nouns for more concrete things are often -а/-я, while more abstract things are often -у/-ю — but that's very imprecise. Or, sometimes people say something like: "If I can see/imagine it as a whole, it probably has -а/-я ending, otherwise — -у/-ю." Also very imprecise.

The Wikipedia article on this subject says that -у/-ю endings are used for:

10. Materials.
11. Collective concepts and names of varieties of fruit trees.
12. Names of buildings, facilities, rooms and their parts, but not architectural details.
13. Names of institutions, establishments, organizations.
14. Vast majority of words meaning place, space, etc., as well as their diminutive forms ending with -к.
15. Natural phenomena.
16. Names of feelings.
17. Names of processes, states, properties, attributes, formations, phenomena of social life, general and abstract concepts.
18. Foreign-origin terms for physical or chemical processes, area parts and so on, also literary terms.
19. Names of games, dances and abstract works of art (music, cinema).
20. Majority of compound suffixless nouns (except animate nouns).
21. Vast majority prefixal nouns (except animate nouns).
22. Names of rivers, lakes, mountains, islands, peninsulas, countries, regions, states. But almost every item of this "rule" has its own set of exceptions.

Even if there were no exceptions — such long and blurred rules are so hard to follow. Therefore genitive endings are usually just remembered on a per-word basis.

Answer 2

Here is a good article on this topic in the Ukrainian language. And, just in case, here is about Second Declension.

About question and from this good article, when use -a, -я:

1. The names of persons, own names and personalized objects and phenomena
2. The names of animals and trees
3. The names of objects and architectural details
4. The names of settlements and planets
5. Other names with emphasis in the genitive case in the final part, as well as extensions присвійності -ов, -ів (-єв), -ин (-їн)
6. What measures of length, weight, time, etc; name of currency; numeric names
7. Names of months and days of the week
8. Names of machines and their parts
9. The terms of foreign origin, meaning elements of the structure of something concrete objects, geometric shapes and their parts and Ukrainian origin Suffixes words-terms

When use -у, -ю:

10. Substances, weight, materials
11. General concepts and titles of varieties of fruit trees
12. The names of the buildings, facilities, rooms and their parts. (except for the names of architectural details)
13. The names of institutions, establishments, organizations.
14. The vast majority of words with the value space, space, etc., as well as their reduced form at -к
15. Natural phenomena
16. The names of feelings
17. The names of processes, states, properties, attributes, formations, phenomena of social life, general and abstract concepts
18. The foreign-origin terms for physical or chemical processes, area parts and so on, also literary terms
19. The names of games, dances and abstract works of art (music, cinema)
20. Majority of compound non-suffix nouns (except animate nouns)
21. The vast majority of prefixal nouns (except animate nouns)
22. The names of rivers, lakes, mountains, islands, peninsulas, countries, regions, states etc.

But, like in any language, almost every item of this "rule" has own set of exceptions. You can see more about this in that article. Therefore genitive endings are usually just remembered on a per-word basis.

Answer 3

Your reference uses animate and inanimate denominations for nouns, but the classic Ukrainian grammar does not qualify nouns for this. We use grammatical gender instead (Masculine, Feminine, and Neuter).

The Second declension group includes nouns that:

1. Masculine Nouns ending with consonant or -о
2. Neuter Nouns ending with -о, -е, -я (with exceptions); also those ending with -ищ-е, -иськ-о

Then, both sections split into "hard", "soft", and "mixed" groups. Here's the above two items expanded:

1. Masculine Nouns ending with consonant or -о
   1. Hard group:
      • ending with consonant (except fricatives ш, ж, ч, дж)
      • ending with -о
      • mostly those ending with -р
   2. Soft group:
      • enging with -ь and -й (also those rare ones ending with -ьо)
      • several of those ending with -ар, -ир
      • several tricky ones that have stress moved to the ending when declined
   3. Mixed group:
      • ending with fricatives ш, ж, ч, дж
2. Neuter Nouns ending with -о, -е, -я (with exceptions); also those ending with -ищ-е, -иськ-о
   1. Hard group:
      • engind with -о
   2. Soft group:
      • ending with -е and -я
   3. Mixed group:
      • ending with fricatives ш, ж, ч, дж + -е
      • ending with -ищ-е, -иськ-о

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Now, when you have everything in place, here's the simple rule:

• Hard group receives -а or -у in Genitive
• Soft group receives -я or -ю in Genitive
• Mixed group receives -а or -у in Genitive