Now that we have examined word classes in detail, we turn to a more basic question: how do we decide what category a word belongs to in the first place? In general, linguists use morphological, syntactic, and semantic clues to determine the category of a word.
The internal structure of a word may give useful clues as to the word’s category. For example, -ness is a suffix that combines with an adjective to produce a noun, e.g., happy → happiness, ill → illness. So if we encounter a word that ends in -ness, this is very likely to be a noun. Similarly, -ment is a suffix that combines with some verbs to produce a noun, e.g., govern → government and establish → establishment.
English verbs can also be morphologically complex. For instance, the present participle of a verb ends in -ing, and expresses the idea of ongoing, incomplete action (e.g., falling, eating). The -ing suffix also appears on nouns derived from verbs, e.g., the falling of the leaves (this is known as the gerund).
Another source of information is the typical contexts in which a word can occur. For example, assume that we have already determined the category of nouns. Then we might say that a syntactic criterion for an adjective in English is that it can occur immediately before a noun, or immediately following the words be or very. According to these tests, near should be categorized as an adjective:
the near window
The end is (very) near. ...