The main grammatical categories are Determiner, Auxiliary, Coordinator, and Complementizer. As also mentioned above, it is hard to define grammatical categories in terms of meaning because they have very little. Their function is to make the lexical categories fit together.
• Determiner (D)
The determiner category includes the articles a(n) and the, as well as demonstratives, possessive pronouns, possessive nouns, some quantifiers, some interrogatives, and some numerals. So, determiner (or D) is an umbrella term for all of these.
Determiners occur with a noun to specify which noun is meant or whose it is. If you are a native speaker, you know how to use the indefinite article a and the definite article the. For non-native speakers, figuring out their use is very difficult. There are four demonstratives in English: this, that, these, and those, with the first two for singular nouns and the last two for plural ones.
a) That javelina loved these trails.
b) Their kangaroo ate my food.
c) Gucci’s food was eaten by Coco.
Possessive pronouns include my, your, his, her, its, our, and their, as in (b). Nouns can be possessives as well, but in that case they have an -’s (or ’) ending, as in (c).
• Auxiliary (AUX)
Auxiliaries are associated with a particular ending, i.e. affix, that appears on the verb immediately to their right. Auxiliary verb functions to help another verb, but does not itself contribute greatly to the meaning of the sentence. Verbs such as have, be, and do can be lexical verbs or auxiliaries.
• Coordinator and Complementizer
Coordinators are relatively simple and join similar categories or phrases. Complementizers introduce subordinate clauses and look remarkably similar to prepositions and adverbs. Complementizers such as that, because, whether, if, and since join two clauses where one clause is subordinate to the other. The subordinate clause is indicated by means of brackets: They are also
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