Examples and Observations:
- "All the words in a language can be broadly divided into two categories, open and closed. The closed category is so called because it does not easily accept new words. Its members are fixed and do not usually change . . .. The open category . . . contains nouns, verbs, adverbs, and descriptive adjectives--exactly those parts of speech that remain open to new additions . . ..
"Words in the open category are usually further divided into simple and complex words. Simple words contain just one morpheme (house, for example, or walk, slow, or green), whereas complex words contain more than one (houses, walking, slowly, or greenest)."
(Thomas E. Murray, The Structure of English. Allyn and Bacon, 1995)
- "Examples of open-class words are those belonging to the major part-of-speech classes (nouns, verbs, adjectives, and adverbs), which in any language tend to be quite large and 'open-ended.' that is, an unlimited number of new words can be created and added to these classes. . . .
"One familiar variety of language in which the distinction between open-class words and closed-class words is important is known as telegraphic speech. The term telegraphic derives from the kind of language used in telegrams, where considerations of space (and money) force one to be as terse as possible. HAVING WONDERFUL TIME; HOTEL GREAT; RETURNING FLIGHT 256; SEND MONEY; STOP. Generally speaking, in telegraphic forms of language the open-class words are retained, whereas the closed-class words are omitted wherever possible."
(Adrian Akmajian, et al., Linguistics: An Introduction to Language and Communication. MIT, 2001)