Category refers to a group of linguistic items which fulfill the same or similar functions in a particular language such as a sentence, a noun phrase or a verb. To determine a word’s category, three criteria are employed.

Word categories often bear some relationship with its meaning. The meanings associated with nouns and verbs can be elaborated by adjectives. For example, when we say that pretty girl, we are attributing the property “pretty” to that girl, and in the sentence “Jenny leaves quickly”, the adverb “quickly” indicates the manner in which Jenny leaves.

The second criterion to determine a word’s category is inflection. Words of different categories take different inflections. Such nouns as “boy” and “desk” take the plural affix -s. Verbs like “work”and “help” take the past tense affix -ed. Although inflection is very helpful in determining a word’s category, it does not always suffice. Some words do not take inflections. For example, nouns like “fog” do not always take plural suffix -s.

The last more reliable criterion of determining a word’s category is its distribution. That is what type of elements can co-occur with a certain word. For example, nouns can typically appear with a determiner like “the girl” and “the card”, verbs with an auxiliary such as “should stay” and “will go”.

A word’s distributional facts together with information about its meaning and inflectional capabilities help identify its syntactic category.