We can refer to something in 3 ways:
According to the Longman Dictionary, if something is definite, it is "clearly known, seen or stated; clear". For example:
"Paris" and "France" are Definite, because you know which things the sentence is about. Just like in this sentence:
Again, you know which picture I have in mind. This, that, these and those are all Definite determiners, just like the.
Context is very important here - we use the if our reader or listener knows which thing we're talking about
Other words can help us clarify which person or thing we're thinking of:
Context is very important, but so is logic:
Similarly with words like the second, the last, the best, the only, the same... :
The last sentence doesn't even identify the student, but logically nobody has more than one biological father. Similarly in this sentence:
Because every sentence has only one subject.
As we've seen, the can be used with all nouns. However, if the listener cannot know which thing we have in mind, we have to use a (or an) with Singular nouns:
With Uncountable or Plural we have two possibilities - we use some when there are a few objects or a little of something:
In other cases we use ∅ (no article):
The way we use logic here is not always... logical. We usually say:
But this can only happen if the possibilities are similar and we don't need to be more definite.
We sometimes expect the listener to guess which thing we have in mind:
It is of course possible that we're wrong and the listener doesn't know or can't guess which thing we're referring to. It sometimes happens in real-life situations:
Possessives are used instead of a, the and some - they can be used for things that are Definite or Indefinite:
Or even to talk about something in general: