Morphologically, most adjectives are gradable. That is, they express the grammatical category known as degree. The basic form of the adjective, which expresses a quality, is known as the positive degree. To express a greater intensity of one of two items, the comparative degree is used, either by adding the suffix –er or with the word more and the basic adjective. To express the greatest intensity among three or more items, the superlative degree is used, either with –est or most.
(5) She can ____.
We will have more to say about auxiliaries later. For now, we can simply note that they are words like can, could, will, would, shall, should, may, might, or must. In most grammar books, auxiliaries are considered a special type of verb, and that is how we will treat them. But it's important to note that auxiliaries do not behave like most other verbs. In particular, they fail most of the tests for verb-hood given here. For example, the frame sentence (5) cannot be filled in with another auxiliary.