How to tell the accusative and dative singular declensions of a masculine noun given the genitive singular declension?

Question

So, I'm trying to create a flashcard list of nouns, and for each entry I want to have all the possible information about that noun. Since this is what most dictionaries do, I figured I would add: The gender of the noun, the nominative singular form, the genitive singular form, and the nominative plural. This should in theory give me enough information to deduce everything else. For example, I can get the dative plural of a noun, given the nominative plural, using the simple rules of: Always add an ‘n’ to the nominative plural, unless the nominative plural already ends in ‘n’ or it ends in ‘s’.

A question then arises, when it comes to masculine nouns (which can be weak or strong), how can one tell the accusative and dative singular declension given only the nominative and genitive singular? I kind of have a theory which so far works with the few nouns I’ve experimented with, but I’m not sure if it can be made into a general rule:

-”If the genitive singular ending has an ‘n’, then the accusative and dative singular are the same as the genitive minus the ‘s’ at the end, if it exists at all. If the genitive ending does not have an ‘n’, then the accusative and dative singular are not declined”.

Some examples of what this looks like in practice (notice that the first element inside the parenthesis represents the genitive singular ending and the second the nominative plural ending):

Der computer (-s, -): The genitive ending does not have an ‘n’, therefore the accusative and dative are not declined. And indeed that is right.

Der Mann (-es, ¨-er): The genitive ending does not have an ‘n’, therefore the accusative and dative are not declined. And indeed that is right.

Der Nachbar (-n, -n): The genitive ending does have an ‘n’, therefore the accusative and dative are the same as genitive without the ‘s’. But since the genitive does not have an ‘s’, the accusative and dative endings are exactly -n. And indeed that is right.

Der Mensch (-en, -en): The genitive ending does have an ‘n’, therefore the accusative and dative are the same as genitive without the ‘s’. But since the genitive does not have an ‘s’, the accusative and dative endings are exactly -en. And indeed that is right.

Der Glaube (-ns, -n): The genitive ending does have an ‘n’, therefore the accusative and dative are the same as genitive without the ‘s’. This means that the dative and accusative ending would be exactly -n. And that is indeed right.

There is one exception I found and that is the noun Das Herz, however this one is kind of in a class of its own, is not even a masculine noun and somehow has week noun-like declensions.

So my question is, is my theory right? Will I encounter some cases where this doesn’t apply? If so, is there any existing rule for one to deduce accusative and dative singular declension while only having the information mentioned above? If not then I might need to add the accusative and dative declension for nouns, so it would look like this: Der Glaube (-n, -n, -ns, -n) (accusative, dative, genitive, plural).

Answer 1

You're right that Herz is irregular and has a unique declension. You're also right that given the gender, nominative singular, genitive singular, and nominative plural you should, with the help of a few relatively simple rules, be able to derive the entire declension table. In addition to masculine nouns with genitive ending -n and those ending -s, there are some which end -ns. Examples are Buchstabe and Name. Some grammars use this as a criterion to distinguish weak/mixed/strong categories for nouns; I don't think this is very helpful for learners, but whichever system you find easiest to learn and use is the one you should follow.

In my notes I have a couple dozen declension classes; I think the most useful form of an answer would be to give examples of each one and you can see if they fit your system and make appropriate changes if not.

1. Masculine, no plural. Example Stolz. Genitive Stolzes.
2. Masculine, no plural ending. Example Engel. Genitive Engels.
3. Masculine, no plural ending, umlaut in plural. Example Apfel. Genitive Apfels.
4. Masculine, plural ending -e. Example Hund. Genitive Hund(e)s.
5. Masculine, plural ending -e, umlaut in plural. Example Gast. Genitive Gast(e)s.
6. Masculine, plural ending -n. Example Doktor. Genitive Doktors.
7. Masculine, plural ending -n. Example Name. Genitive Namens.
8. Masculine, plural ending -n. Example Hase. Genitive Hasen.
9. Masculine, plural ending -r, umlaut in plural. Example Mund. Genitive Mund(e)s.
10. Masculine, plural ending -s. Example Opa. Genitive Opas.
11. Neuter, no plural. Example Laub. Genitive Laub(e)s.
12. Neuter, no plural ending. Example Feuer. Genitive Feuers.
13. Neuter, no plural ending, umlaut in plural. Example Kloster. Genitive Klosters.
14. Neuter, plural ending -e. Example Brot. Genitive Brot(e)s.
15. Neuter, plural ending -n. Example Auge. Genitive Auges.
16. Neuter, plural ending -n. Example Herz. Genitive Herzens.
17. Neuter, plural ending -r. Example Bild. Genitive Bild(e)s.
18. Neuter, plural ending -r, umlaut in plural. Example Buch. Genitive Buch(e)s.
19. Neuter, plural ending -s. Example Auto. Genitive Autos.
20. Feminine, no plural. Example Zier. Genitive Zier.
21. Feminine, no plural ending, umlaut in plural. Example Mutter. Genitive Mutter.
22. Feminine, plural ending -e. Example Trübsal. Genitive Trübsal.
23. Feminine, plural ending -e, umlaut in plural. Example Hand. Genitive Hand.
24. Feminine, plural ending -n. Example Woche. Genitive Woche.
25. Feminine, plural ending -s. Example Oma. Genitive Oma.
26. Plural only ending -e. Example Leute.
27. Plural only ending -n. Example Eltern.
28. Plural only ending -r. Example Trümmer.
29. Plural only ending -s. Example Pommes.

This does not account for a few nouns whose gender and declension can change depending on the meaning or other factors, for example See. There are some possible classes that I haven't listed, which may mean that they or empty or just that I haven't found an example yet or that the only examples I've found are too rare to mention.

PS. Don't forget about nouns formed from adjectives; these have their own declension pattern.