This post will introduce you to grammatical cases. English has 2 cases (the subject case and the object case). However, their forms are different only for pronouns ("we" vs. "us").
Cases are forms of words when used in various places in a sentence (subject, object, indirect object, etc.)
If the sentence "Ivan is writing a letter to Ana." is translated into Croatian, all three nouns (Ivan, letter, Ana) must be put in cases corresponding to their roles. In English one uses just word order and preposition "to".
Case changes apply to nouns, adjectives and pronouns. For instance, the phrase moja sestra "my sister" (adjective + noun) and the pronoun ona "she" change like this:
Moja sestra je ovdje. "My sister is here" Ona je ovdje. "She is here." Vidiš moju sestru. "You (can) see my sister" Vidiš je. "You (can) see her."
We see that the adjective moja and the name change only a bit (only the ending), but the pronoun changes completely (this is actually similar to English, where "she" changes to "her" — a complete change). This example illustrates only two cases, but that's the principle.
So, a noun has different forms in various cases, an adjective has them too, but generally they don't follow the same pattern (although they are similar). Even worse, the pattern for an adjective depends on the gender of the noun! (That's actually the definition of gender I'm using here: it tells you which form of an adjective you should use).
As we've seen from the example, pronouns have yet another pattern... This is a hard thing to learn, and there's no other way but to memorize it. Therefore, it's worth learning the often used cases first. This chapter will introduce you to the cases, and the next two chapters will introduce forms for adjectives and nouns for the two most often used cases, and we will leave pronouns out for now.
Cases are roles of words in sentences.
Nouns ("cat"), including names ("Ivan"), adjectives ("big", "my") and pronouns ("I", "you") have different forms in various cases according to specific patterns.
I don't want to oversimplify things. Cases are a hard-to-learn concept, and which case is used where even harder. So I want to introduce basic cases as soon as possible. Don't be impatient and jump into conclusions, you must learn gradually where each case is needed and how to put a word into that case!
Some languages have more than 10 cases, like Hungarian. Georgian, Latin, Old Greek, Sanskrit, Old English, and most Slavic languages have 5-8 cases. Most textbooks say that Croatian has 7 cases.
Cases are woven together with singular/plural, so every Croatian noun has 7 forms for cases in singular, and additional 7 for plural = 14 all together. Adjectives have even more forms — one for each gender and case combination! Hopeless? Not completely.
A Quick Survey
First, one case (the nominative, or 'subject case') is the 'default' case — you have to know the dictionary form of a noun if nothing else, and there are rules how to make a plural. So, 6x2 left.
Second, two of the remaining 6 cases are always exactly the same in both singular and plural (except for a small difference in accent; also they are not equal in some dialects); they are called locative and dative — I'll call them both 'dative'. We are down to 5x2.
Next, there is a case (the vocative) used only when calling someone, or yelling at someone (like in "John, come down!" or "You, idiot!"); we can live without it for a while, and yell in nominative. Besides, a vocative plural is always the same as the nominative plural (there's again a small difference in accent for some words). Did you know that in fact, many languages have special forms for yelling and giving orders? This leaves us with 4x2.
We can postpone learning of two more cases — the before mentioned genitive (which is in many aspects the most difficult case!) and instrumental — because they are not used in simplest sentences; they are however used in some constructions, and we will have to learn them a bit later (otherwise we would not be able to say "two apples" in Croatian).
(The genitive case is introduced in 13 Genitive Case, and the instrumental case is introduced in 21 Instrumental Case. The vocative case is explained in 41 Imperatives, Permissions and Vocative Case.)
This leaves us with just 2x2 cases — precisely one for objects (the accusative), and another for indirect objects ('to-case', before mentioned dative). And, of course, there's the default case found in every language — the nominative. Sorry, I cannot make it simpler than that!
And you don't need to remember all 6 forms for every noun — there are rules how to make all of them.
Cases are usually abbreviated to three letters (e.g. acc. = accusative) or to one letter (N = nominative, A = accusative, etc.), and singular and plural to sg. and pl.
If you are worried about the locative case and how it got lost and absorbed into the dative case, you are free to call that case dative/locative. In practice, in colloquial conversation they are always identical. Let's keep things simple.
How They Work
Let's take a look how the noun Ana (a personal name) looks in various cases. I will indicate cases with superscribed letters N (nominative), A (accusative) and D (dative):
Ana(N) jede. "Ana is eating."
Hranim Anu(A). "I am feeding Ana."
Pišem Ani(D). "I am writing to Ana."
This doesn't look too complex! Don't forget, the nominative is the 'normal', unchanged form. From standpoint of Croatian, you could say that English nouns are always in the nominative case.
Now, some fun: every noun must be squeezed into this scheme! So, if one is writing to somebody else, let's say, to George Bush, it will be:
George(N) Bush(N) piše Ani. "George Bush is writing to Ana."
Pišem Georgeu(D) Bushu(D). "I am writing to George Bush."
You may also note two things: first, we changed every word in his name (that's normal); second, we added -u and not -i as we did to Ana (that's because Ana ends on -a, and we really changed that -a to -i).
Warning: most verbs use accusative, and some can use dative (like "write", "give"). But not all. That's not important at this time, but just remember that use of cases ultimately depends on the verb. The verb is the boss.
There's another use for acc. and dat. They are used with prepositions (words that correspond to English "in", "on", etc.). Croatian has a system of prepositions that is not too different from English (there are languages without prepositions!), and quite similar to German. The main point is that after a preposition a noun must be put in appropriate case. However, for some prepositions we can use more than one case, and that affects the meaning:
u + D = "in something" u + A = "to something" na + D = "on, at something" na + A = "onto something"
In short, with these two prepositions (u, na), the accusative is used with directions (u grad "to the city"), and dative with static locations (u gradu "in the city"). German speakers will recognize a lot of similarities.
Summary and Final Remarks
Nominative is the default, "dictionary" case, and is used as a subject of sentence ("she is writing").
Accusative case is used as an object ("feed her"), and with prepositions u, na meaning motion to somewhere ("to", "onto").
Dative case is used as an indirect object ("write to her"), and with prepositions u, na meaning static location ("in", "on", "at").
Please, bear in mind these are only some uses of those cases. There are of course more. Much more :)
Don't ever think that acc. itself means 'direction'. It gets such meaning only with several prepositions. And there are other prepositions that require accusative but don't mean directions! That's why it's a complex thing to learn. (Again, exactly the same complexity exists in German).
Many people in Croatia always list cases in the 'standard' order (nom., gen., dat., etc.) That's a very bad choice since it makes cases much harder to learn (you'll see later why). I decided to completely disregard the so-called standard order. If hear from anyone that there's 'the standard order of cases', please ask that person to explain reasons for it, and they will not be able to say anything (except that it's a tradition).
Finally, you will maybe read somewhere that cases 'answer to questions'. That's the way Croatian children are taught cases in school. However, such approach is useful only if already you know Croatian — as children do — but you don't know the names of cases. For instance, the page learn-croatian.com gives a completely useless introduction to cases, and even tells that the word školu is in the locative case, while it's of course in the accusative case (I'll show you case patterns soon, so you'll be able to figure it out yourself). If you find any resource for learning Croatian mentioning 'cases answering to questions', you can safely conclude that their author didn't understand what cases really are, and you can safely disregard it...
Updated 2013-11-06 (v. 0.4)