• The articles, “the,” and “a,” are central determiners. “The” is a definite article and “a” is an indefinite article.

Singular count nouns must be preceded by an article unless they are preceded by another central determiner such as “this,” “my,” “which,” or “no.” Whether a definite or an indefinite article is placed before a singular noun is a matter of identifiability: if the “referent” of the noun (i.e. the thing to which it refers) is identifiable by the listener or reader, then a definite article is used; if it is not so identifiable, then an indefinite article is used. The status of identifiability can be achieved in a variety of ways:

1. because of the situation: The salmon salad is supposed to be very good. [said in a restaurant, for example]
2. because of “general knowledge”: The sky is very beautiful this evening.
3. because of linguistic information given earlier (“anaphoric reference”): Jill ordered a cup of coffee and a dessert, but she didn’t touch the dessert.
4. because of linguistic information given later by the post-modification of the noun (“cataphoric reference”): The woman sitting next to me was drunk.
5. because of reference to a unique institution of society “present” at various times and places (“sporadic reference”): Harry and Sarah share a great love of the theater.
6. because reference is made to something that is logically unique: Harry is sure “The Wall Street Journal” is the best newspaper in the world.
7. because reference is made to a body part: Harry kissed Jill on the cheek.

Plural count nouns are preceded by the definite article “the” or by no article at all. (The indefinite article “a,” is used only with singular count nouns.)

- Because indefinite articles cannot be used with plurals, the distinction between definite and indefinite reference is made in other ways: either by using no article or by using the central determiner “some,” as a sort of substitute: Jack heard (some) dogs barking in the distance. He didn’t realize at the time that the dogs were Harry’s.
- Plural count nouns are commonly used to achieve generic as opposed to specific reference (I.e. reference to a type of thing rather than to a particular thing). When they are used in this way, they are never preceded by an article: Dogs are more popular than cats. (It is not possible to insert “some” before either of the two plurals in this sentence because they refer generically (not specifically) to those types of animal.)

Non-count nouns are preceded by the definite article “the,” or by no article at all.

- Non-count nouns are comparable to count noun plurals in the matter of article use: when used to make a specific reference, they are preceded by “the:” The beer Jack bought is in the fridge. But they cannot be preceded by “a” when used indefinitely. Instead, they are either not preceded by any determiner or they are preceded by the central determiner, “some: ”Harry spilt (some) oil on the table.” Here too, the optional use of “some” is only possible when the reference is specific; “some” cannot be placed before “oil” in the following sentence where it is used generically: Harry made his fortune by buying and selling oil.
- There is a complication, however, in the case of abstract non-count nouns. Because they are always generic, the definite/indefinite distinction is not logically relevant. But it does play a grammatical role: when the scope of an abstract non-count noun is retricted by postmodification, it is preceded by an article: Dick is interested in the history of Italy. (Because the sentence, Dick is interested in Italian history, has exactly the same meaning, there seems to be no logical explanation for this phenomenon, but it is a well-established feature of English.)