2.2 Not all word classes can be expanded
The word classes you’ve looked at since Week 1 are the open classes. You’ve touched on pronouns and determiners, and you met modal auxiliaries and auxiliary verbs in Week 3. These smaller word classes are examples of what we call closed class words. These words don’t so much refer to things in the world, but rather act as a ‘glue’ to join the open class words together into phrases and sentences that mean something. You might also hear this type of word called function words or grammatical words.
Closed class words are small in number (and often in length), but they are very important in communicating meaning. Consider the difference made by the bold word in these sentences:
That’s not true! (what if …not wasn’t there?)
That’s my money (what if it was his, her or their?)
She wants that one (what if it was this?)
You have to stay here (what if it was I or we?)
Closed classes don’t change as readily as the open classes and they aren’t receptive to new words. The stability of the closed classes is important for communication and for language teaching.
The closed class words are mainly pronouns, determiners, prepositions, conjunctions and auxiliary verbs. Some of the names for these classes may be new to you if you haven’t studied grammar before, but you will soon see that the words they contain are very familiar.