ABSTRACT
Though in the previous chapter our attention was centred on the formation of single concepts, each of these by its very nature is embedded in a structure of other concepts. Each (except primary concepts) is derived from other concepts and contributes to the formation of yet others, so it is part of a hierarchy. But at each level alternative classifications are possible, leading to different hierarchies. A car can be classed as a vehicle (with buses, trains, aircraft), as a status symbol (with a title, a good address, a mink coat), as a source of inland revenue (with tobacco, drink, and dog licenses), as an export (with gramophone records, Scotch whisky, Harris tweed), etc. What is more, the class concepts on which we have been concentrating so far are by no means the only kind. Given a collection not of single objects but of pairs of objects we may become aware of something in common between the pairs. For example:
puppy, dog; kitten, cat; chicken, hen.
