Halliday & Matthiessen (1999: 448):
The problem of classifying qualities is often approached grammatically as a question of word classification: are adjectives funny verbs, funny nouns, or a completely distinct word class? All three questions have been asked, and all three answered in the affirmative. The questions themselves reflect one of the biases of traditional grammar: it is based on words. Our approach is a functional one, which does not start with word classes taken out of context; … Semantically, the relevant question is how a figure is organised in English. This allows us to look at qualities ‘from above’, keeping their semantic environment in view.