There are, however, several grammatical classes that are not true adjectives but are included under the broad traditional umbrella of adjective, which cannot serve as adjective phrase heads. Most of these can be included in a broad class called determiners. Determiners are usually easy to differentiate from true adjectives because they do not head adjective phrases. But there is some fuzziness. Is it a determiner or an adjective.
Some grammarians avoid the fuzziness by calling it a quatifier .
I'd rather not do that. Instead, I' ll just deal with them individually. Functionally, true adverbs head adverb phrases. Their function is simply to modify. Semantically, adverbs answer modification questions regarding time, place, manner, frequency, and degree.