I have problems with the linguistic terms. I did not find satisfactory explanation about "referentiality". On the other hand, what are the differences between "case" and "referentiality"? If there is, I want to learn their features. Can you explain me with some examples.
Referentiality has to do with how identifiable a referent in an utterance is. A referent is normally a noun phrase such as "my cat", or "them", but maybe it could be something else, I'm not sure.
Referentiality can mostly define the definiteness and specificity of a referent. In English "the" is the definite article and "a" or "an" is the indefinite article. When something is definite it means that the speaker expects the hearer to understand exactly which thing the speaker is referring to. There are more ways to mark a definite noun phrase than just "the".
- I saw the queen yesterday! (Presumably the queen of whatever country you are in, or maybe the queen is visiting your country and this is well known.)
- Now mix the egg and flour together. (Previously mentioned in the recipe.)
- Where is Johnny? (Proper names are definite.)
- He told me to give this to you. (Pronouns are usually definite.)
- My car is being repaired. (Possessed noun phrases are definite.)
- Stop that man! (NPs marked with demonstratives are definite.)
- I am a linguist.
- Drink some water.
- Cows are mammals.
- You can have one cookie.
- There are several people outside.
- Someone called and left a message.
- Then all of a sudden this guy came out of nowhere...
In all these indefinite examples the speaker does not expect the hearer to be able to identify a specific item or person. Even in the first example although the speaker is referring to himself "a linguist" is just a general role being applied to "I", similar to 3. Normally numbered noun phrases are indefinite even when the number is "one". In 4, the listener is only allowed one cookie, but they can choose any of the available cookies, unless the speaker said "You can have that one cookie." Example 6 uses an indefinite pronoun (like everyone, nothing, anywhere). Indefinites are usually just indefinite the first time you mention them, and then after that they can be referred to definitely.
Generally things are definite either because we already mentioned and identified them early in the discussion/text, or it is shared knowledge between the speaker and listener "Mom", "the mayor", or because it is something that is generally known, like "the moon".
Specificity is about whether the speaker is able to identify the referent or not. (At least that is how I understand it.) It makes sense that normally definite noun phrases are specific, because if the speaker can't identify the referent then they usually don't expect the hearer to do so. But there are exceptions.
- Take me to your leader. (definite but non-specific, if the speaker doesn't know who the leader is.)
- We should order some pizzas. (indefinite, non-specific, the pizzas don't even exist yet!)
- I have a son and a daughter. (indefinite, specific)
The last example is a pretty common situation where the speaker knows what they are talking about but they are just telling the hearer for the first time so they don't expect them to know the referents already. Specificity is more tricky than definiteness and less likely to be marked grammatically in a language (English does not mark it), because languages need to accommodate more to what the hearer knows or doesn't know, for successful communication, rather than what the speaker knows.
So referentiality has a lot to do with information transfer between speakers. I think there is more to referentiality than just definiteness and specificity, but those are the big things. Case is something completely different and is about the role that noun phrases play in a sentence like subject or object. You can easily find more about that by searching for "grammatical case" online.