How should I form grammatical cases in my conlang?

Question

Now, I'm a Latin student, and that being said, I understand how cases operate and what they do for a language, but I've never enjoyed learning/studying/keeping track of them. That being said, I feel like my conlang needs at least a simple case system. Question is: should I try and base it off of what I'm familiar with (English and Latin), or can I make my own (albeit extremely watered-down) system? Example: having one noun case that is its name in any instance (whether it's the subject, object, etc.), a case indicating possession: "something of the noun", a vocative case, and maybe some other simple cases.

Answer 1

Latin's case system is fairly standard for Indo-European languages. But it's by no means the only option even within that language family.

• At most, English has nominative, accusative, genitive, and possessive. Only the pronouns still distinguish them: they, them, their, theirs. (In general English has no noun cases at this point, except for arguably the 's particle—but that's a separate debate.)
• German has nominative, genitive, dative, and accusative: he, his, to him, him.
• Russian also has similar cases to Latin, but the ablative is split into the prepositional (object of some prepositions) and the instrumental ("using ___").

If you look at non-Indo-European languages there are even more possibilities.

• Mandarin Chinese has no cases at all.
• Finnish has fifteen, such as the elative ("out of the house"), the illative ("into the house"), the allative ("to the house"), the ablative ("from the house"), and the translative ("turning into a house").
• Basque (sometimes) divides ergative-absolutive rather than nominative-accusative: in other words, the subject of an intransitive verb looks like the object of a transitive verb.
• Japanese and Korean have two types of nominative, the "subject nominative" and the "topic nominative".

In general, cases tend to "appear" in the following order, in that the later ones usually aren't found without the earlier ones. But there are lots and lots of exceptions to this; it's more of a general guideline than a rule.

• Nominative/ergative
• Accusative/absolutive
• Genitive
• Dative
• Prepositional
• Ablative
• Instrumental
• Vocative
• Anything else (looking at you, Finnish)

Answer 2

In a conlang, you can essentially try out whatever you want. When you want to go for a naturalistic, but simple case system, there are are languages with just two cases termed nominative (for the subject of a sentence) and oblique (for everything else, including direct and indirect objects as well as nouns in prepositional phrases).

Answer 3

One personal example: my mother tongue has no case structure and most people I know do not speak a language that has a real, rough case system like Latin. After I learned some languages that had cases I felt the need to create a conlang with a very simple case structure in order to teach my friends what cases were. Now, most of them already spoke English, so I decided to make a conlang based on English. After thinking a little about colours and numbers, I created the following structure:

1. Nominative
2. Genitive
3. Accusative
4. Locative

Those were the easiest cases to explain. The numbers represent them. This means that we can translate a simple sentence like

Michael knows the place in which Olivia's apples were.

to

Michael-1 knows place-3 which-4 Olivia-2 apples-1 were.

Now, the numbers can be translated to sounds:

1. No sound
2. -'s
3. tow
4. ins

And get

Michael knows placetow whichins Olivia's apples were.

where I tried to emphasize word ordering is mostly secondary in case-rich languages.