As an English speaker learning German, the tendency of native speakers, textbooks & online resources to explain cases simply by repeating their names is frustrating & confusing. Stating "this is nominative, while this is dative" does nothing to explain the purpose or concept. Might as well say "this is blargle, while this is schmergelpluff" - equally meaningless, which is why I still struggle w/these concepts :)
So, with that in mind, and because I'm curious to see whether or not I actually have a good grasp of them myself...
What are "cases"?
A case is 1 of the possible "declensions," in a language.
Well, that doesn't help. So...
What is "declension"?
A declension is a grouping of word endings/changes that help to clarify the role each noun or pronoun plays in a sentence, removing possible ambiguity:
- Who/what is doing a verb?
- What thing is having a verb done to it?
- What other thing is being used to do the verb to the main thing?
- For whom or what is the thing being done?
- Who owns or possesses the thing?
- Where is the verb happening; are the doer(s) or the thing(s) moving or stationary?
- Are the doers or things being addressed by proper nouns?
Each such situation is a separate "case," and each case has a particular name.
If you know what the case names mean, you can use them to infer/label the purpose for each noun/pronoun in the sentence (if not, you're likely even more confused than when you started).
Ok, so now what are the "cases"?
German, as you noted, has 4 cases (4 Fälle).
Each case (Fall) can be thought of as the following:
- Nominative (Nominativ): The subject of the sentence. Who/what does the verb?
- Accusative (Akkusativ): Direct Object. The thing having the verb done to it.
- Dative (Dativ): The indirect object. With or for what 2nd thing is the verb being done to the 1st thing?
- Genitive (Genitiv): Who/what possesses the thing, and who/what is possessed?
(Not used in German, at least not anymore:)
- Locative: Where is the verb happening? The place noun, I think?
- Ablative: Stationary or moving? Related to prepositions, which work a bit differently in German.
- Vocative: A proper noun (name) for the doer or the thing.
How do I tell what's what?
Now that you know which role a noun/pronoun plays (its case), you know which "inflections" or changes to apply to it and its related parts.
In German, the specific preposition often requires/dictates which case a noun takes, whether accusative, dative, or genitive, so if you memorize what case must go with a given preposition, you can remove a lot of the guesswork from considering the role of the noun & just use what you're told is the required case.
How do I know what to change to and how?
Inflection is the process of changing a word to reflect a particular grammatical role - a different case, plurality, tense, gender, etc. For verbs, this is also called "conjugation."
Inflection is what's happening when changing the masculine definite article "der" into "den", "dem", or "des" depending on the (pro)noun's case or role in the sentence. It's also what happens when changing a singular "der" to a plural "die."
Key tip: An article, adjective, pronoun and noun itself all must change to match the same case, on a noun-by-noun basis.
So what semantic information does this help to convey?
In addition to clarifying the noun's role in the sentence as explained above, also:
- How many doers are doing the thing, and are there multiple things?
- What gender (either in an actual biological sense or in the often arbitrary linguistic sense) are the doers and the things?
- Which descriptive words apply to the doer and which to the things?
In English this information typically only requires pluralizing the noun/pronoun.
In German, you must also change the article, because the noun doesn't always change.
Das Mädchen = the girl ... Die Mädchen = the girls
So why do I care?
Without these sorts of changes, the nouns can remain ambiguous, because German allows you to change the word order around in various ways that aren't possible in English.
Den Hund beißt der Mann.
If you don't recognize the cases & changes in articles, an English speaker might interpret this sentence from left to right as "The dog bites the man."
This is incorrect, because the sentence actually says: "The man bites the dog."
Den Hund (note the accusative article, indicating that this noun receives the verb) beißt der Mann (nominative article, indicating the Man is doing the verb).
This is equivalent to "Der Mann beißt den Hund," but places an emphasis on the fact that it was the dog (as opposed to something else) that the man bit.
Another example with pronouns could be:
"Er sieht sie." - He sees her.
"Sie sieht er." - He sees her. (Her, he sees).
"Sie sieht ihn." - She sees him.
"Ihn sieht sie." - She sees him. (Him, she sees).
By using cases and proper inflection, you can remove ambiguity, and also be sure exactly which noun is doing what to other nouns, regardless of the actual order of words in the sentence.