Determiner

A determiner is a class of words that typically functions as a determiner (function) in noun phrases. As such, they establish the reference of a noun or noun phrase, including quantity, rather than its attributes as expressed by adjectives. Despite this tendency, determiners have a variety of functions including, in English, modifiers in adjective phrases and determiner phrases, and even markers of coordination.
This word class, or part of speech, exists in many languages, including English, though most English dictionaries still classify determiners under other parts of speech. Determiners usually include articles, and may include items like demonstratives, possessive determiners, quantifiers, and cardinal numbers, depending on the language.

English determiners

Determiners, in English, form a closed class of words that number (exclusive of cardinal numerals) about 50 and include^[1]:

• Alternative-additive Determiners: another, other, somebody else
• Articles: a, an, the
• Cardinal Numbers: one, two, fifty, etc.
• Degree Determiners: many, much, few, little...
• Demonstratives: this, that, these, those, which
• Disjunctive Determiners: either, neither
• Distributive Determiners: each, every
• Elective Determiners: any, either, wichever
• Equative Determiners: the same
• Evaluative Determiners: such
• Exclamative Determiners: what eyes!
• Existential Determiners: some, any
• Interrogative and Relative Determiners: which, what, whichever, whatever
• Negative Determiners: no, neither
• Personal Determiners: we teachers, you guys
• Positive-multal Determiners: a lot of, many, several
• Positive-paucal Determiners: a few, a little, some
• Possessive Determiners: my, your, our, etc.
• Qualitative Determiners: that
• Quantifiers: all, few, many, several, some, every, each, any, no, etc.
• Sufficiency Determiners: enough, sufficient
• Uniquitive Determiners: the only
• Universal Determiners: all, both

The two categories into which every one of these determiners can be classified are those of the definite determiners, which limit their reference back to a specific already mentioned entity, and the indefinite determiners, which broaden their referent to one which has not been previously specified, or has just been newly introduced into discourse.
While many words belong to this lexical category exclusively, others belong to a number of categories, for example, the pronoun what in What is good as opposed to the determiner what in what one is good. While numerals exist as nouns, it is debated whether numerals are determiners or not^[2]. For instance, the English numerals for 100 or larger need a determiner, such as "a hundred men." Similarly, while pronouns like my, your, etc. function as determiners in a noun phrase, many grammars do not make the distinction between class and function and so lump these in with determiners.