Qualitative and classifying adjectives
Not all adjectives have a comparative and superlative form nor can they all be graded. This is because there are two types of adjective, known as qualitative and classifying.
Qualitative adjectives describe the qualities of a person or thing – whether they are large or small, happy or sad, etc. This type of adjective is gradable. For example:
a fairly tall man
a very boring film
a really long vacation
an extremely expensive car
Classifying adjectives place people and things into categories or classes. Do you read a daily newspaper or a weekly one? Does your house have an electric oven or a gas oven? Here are some more examples of classifying adjectives:
the western hemisphere
an annual event
the external walls
a nuclear weapon
Classifying adjectives don't generally have comparative and superlative forms. It would sound strange to describe one event as "more annual" than another, for example, or one weapon as "the most nuclear." In general, classifying adjectives are also non-gradable. An event cannot be "very annual" nor an oven "fairly electric."
See the OxfordWords blog for more about gradable and non-gradable adjectives.
Read more about adjectives: