So far, we have been looking at Form Class Words – nouns, verbs, adjectives, and adverbs. To review, form class words are words that can change their shape by accepting morphemes. So a noun, like dog, can become dogs; and an adjective like happy can become happier, or unhappy.
Form class words also have lexical meaning. This means that their primary job is to transmit semantic content – to tell us (for instance) that the dog is happy or unhappy, or brown, or a beagle.
In opposition to these words, we have structure class words. While these words do carry some semantic content, the main purpose of structure class words is to transmit grammatical relationships.
Structure class words include
What do we mean when we say that these words transmit grammatical relationships? Consider this sentence:
Elvis and Ivy gave that biscuit to the puppy on the table.
The structure class words are all underlined. While the words do carry some semantic meaning, what they are mainly doing is telling you, as an English speaker, how to connect these words grammatically to one another.
Consider the same sentence, for instance, without the structure words, or with incorrect structure words:
Elvis Ivy gave biscuit puppy table.
Elvis but Ivy gave itself biscuit be puppy with six table.
Besides having a function that is mainly grammatical, structure class words differ from form class words in two other ways.
(1) For the most part, they do not change their shape. They don’t take plurals, the verbs among them do not shift tense, they can’t take any morphemes.
(2) They are essentially a fixed set, to which no new members are likely to be added; and this set is relatively small. While the set of nouns, in contrast, is huge, and ever expanding, we can list most of the prepositions in English in one box on one page of your text.