Closed- System Items

The parts of speech are listed in two groups (a) and (b), and this introduces a distinction of very great significance. Set (b) comprises what are called "closed-system" items. That is, the sets of items are closed in the sense that they cannot normally be extended by the creation of additional members; a moment's reflection is enough for us to realize how rarely in a language we invent or adopt a new or additional pronoun. It requires no great efforts to list all the members in a closed system, and to be reasonably sure that one has in fact made an exhaustive inventory. The items are said to constitute a system in being (1) reciprocally exclusive: the decision to use one item in a given structure excludes the possibility of using any other and (2) reciprocally defining: it is less easy to state the meaning of any individual item than to define it in relation to the rest of the system. This may be clearer with a non-linguistic analogy. If we are told that a student came third in an examination, the "meaning" that we attach to third will depend on knowing how many candidates took the examination: "third" in a set of four has a very different meaning from "third" in a set of thirty.