English flat adverbs and adjectives

The boundaries and the complementarity of the adjective and adverb word classes in English are blurred in standard English by the existence of a limited number of flat adverbs, i.e. adverbs that are homonymous with existing adjectives (e.g. early, hard, long, plain). Unlike what happened with other word classes, the status of these words as full-fledged adverbs has never been questioned despite their resemblance to adjectives and their limited syntactic distribution. This article analyzes 37 words traditionally recognized as flat adverbs in standard English through 100 grammatical properties, and compares them to clearly established adjectives and adverbs. A hierarchical clustering analysis shows that most of the words under study actually cluster with adjectives, since they have most, if not all, typical adjectival properties (‑ly-suffixation, gradability, attributive and predicative functions), and only one or two adverbial properties (adjunct function in end position, and sometimes degree modifier of adjectives). It can therefore be assumed that most “flat adverbs” are not adverbs converted from adjectives, but rather adjectives that have one or two additional functions which are traditionally devoted to adverbs in English. This analysis preserves the orthogonality of word class and syntactic function, and accounts for the emerging use of an increasing number of adjectives in informal contemporary English.