A determiner is a word that introduces a noun. It always comes before a noun, not after, and it also comes before any adjective used to describe the noun.
Determiner suggests the context in which noun is used whether it is ownership, quantity or relative location. Determiners always come first in the noun phrase.
Generally, an indefinite article (a or an) is used before singular nouns. When speaking about singular or plural nouns specifically; definite article, demonstrative pronoun, possessive pronoun or quantifier is used.
Determiners can be divided into two groups:
Articles specify (or determine) which noun the speaker is referring to. A and an are indefinite articles and are used for a general noun.
Examples:
In these examples, the sentence is talking about dogs or ostriches in general, meaning any dog. Note that ‘a’ is used before words that begin with consonants while ‘an’ is used before words beginning with vowel sounds.
On the other hand, the is a definite article, meaning the speaker is referring to a specific noun.
Examples:
Here the speaker is referring to a particular dog and a particular restaurant. It's not a general category, but only one animal or place that's important. When your meaning is specific, use a definite article.
Demonstrative pronouns are also used as determiners in English. There are four of them: this, that, these and those.
Examples:
When referring to a noun that belongs to someone or something, possessive pronouns are used to show ownership. Possessive pronouns include my, your, his, her, its, our, one’s, whose and their.
Examples:
As always, the determiner comes before the noun and any modifying adjectives.
We cannot put two determiners from Group A together.
Examples:
Mostly, this category includes Quantifiers.
Quantifiers indicate how much or how little of the noun is discussed.
The following quantifiers work with countable nouns:
Few tree trees
The following quantifiers work with un-countable nouns:
The following quantifiers work with both countable and un-countable nouns:
A lot of trees/dancing
Lots of trees/dancing
Plenty of trees/dancing
Note that ‘all’ can be used with other determiners to specify which particular items are meant (i.e. all the books in this pile). In this case, the quantifier always comes before the article or demonstrative. It is also possible to use ‘all’ alone to refer to items generally (i.e. all books on the table needs dusting)
Examples:
(many, few, some are determiners which do not need nouns)