What are word classes?

We have used terms such as ‘noun’, ‘adjective’, ‘adverb’, ‘verb’ and ‘preposition’ without defining them. The terms are in everyday use and everyday definitions are available, such as nouns being the names of persons, places and things and verbs being the names of actions or states. These definitions contain a grain of truth but are inadequate for serious investigation of English or any other language. One weakness is that they appeal in a superficial way to only one part of meaning, the kind of things that a given word denotes. ‘Semantic criteria’, it is important to take account of what speakers and writers actually do with verbs, nouns and so on. (The term ‘denote’ is used for the relationship between a given word and the set of entities, in the broadest sense, to which it can be applied. Traditional dictionary explanations of the meaning of individual words can be thought of as embryo descriptions of denotations. we see that, for example, nouns are the center of noun phrases, by means of which speakers and writers refer to entities.)

Another weakness is that they ignore the business of where a given word is placed in a clause or phrase, a topic which was introduced in the discussion of phrases , but which is also important for the analysis of words. For a given word, we can investigate what words it typically combines with in phrases, what types of phrase it occurs in and where these types of phrase occur in clauses. For instance, nouns can be preceded by words such as the, a and this but verbs cannot.  Adjectives can precede a noun, as in new books, or follow certain verbs, as in is new, seemed new. Verbs occur in different slots in the clause. That is, we transfer from humans to words the precept that you know them by the company they keep and group them into classes, hence the term ‘word classes’.

We appeal first to a very old distinction between words that have a denotation and words that do not. Words that have a denotation apply to people, places, things (in the broadest sense), actions, states and properties. They are known as lexical or content words, and in English include nouns (e.g. villa, baby, idea), verbs (e.g. buy, destroy, think), adjectives (e.g. wooden, strong, abstract) and adverbs (e.g. rapidly, hopefully). Words that do not refer are known as grammatical or form words. (‘Lexical’ usually contrasts with ‘grammatical’, ‘content’ with ‘form’.) Grammatical or form words in English are the definite and indefinite articles the and a, the demonstrative adjectives this, these, that and those, the auxiliary verbs is, has and so on (as in is reading a book, has read this book). (The term ‘auxiliary’ reflects the fact that these verbs do not refer to actions or states but ‘help’ main verbs such as read to build a construction.)

Many accounts of word classes in English treat verbs such as may, could and must and prepositions such as with, from and by as grammatical words, but these seem to be on the borderline. In the days before widespread telephone communication and before the invention of fax machines and e-mail, urgent messages were sent by telegram. Each word cost a certain amount, and to keep down the cost of the whole telegram people put in only those words essential for the message to be interpreted correctly. For instance, instead of We are arriving on Tuesday at 5pm the telegram would read Arriving Tuesday 5pm. The words that typically turned up in telegrams were nouns, verbs and (less often) adjectives and adverbs, namely content words. Articles, demonstrative adjectives, auxiliary verbs and prepositions were typically left out.

The problem is that, in spite of the telegram test, the distinction between Press the button above the green light and Press the button below the green light is rather important; the prepositions above and below cannot be left out, because a wrong interpretation might lead to just as regrettable consequences as the difference between Press the red button and Press the green button. What the telegram test shows is that some missing words can be easily guessed while others cannot. Prepositions such as on and at in time phrases have no competitors – the sender of the telegram might have meant after 5pm, but we would expect after or before to be stated explicitly in the message. Prepositions such as below have competitors such as above, next, by, opposite; recent analyses of prepositions have shown that many have major meanings and can only be described as words with denotations. Equally, we must concede that the meaning of a preposition such as of is hard to establish. For these reasons, and in spite of the telegram test, prepositions (along with modal verbs such as can and must) will be regarded as lexical or content words. In this class of lexical items, they are not as central as nouns, say, but they are not grammatical items either such as the and a.