last changed in 2002
Relations are links between nodes. There are two kinds of relation.
A. The simplest relation is 'isa', the relation used for classifying one concept as an example or sub-class of another - for example,
 John isa linguist.
 Noun isa Word.
This relation is absulutely fundamental to the whole of thought as it is the basis for classification and generalisation by inheritance. It is not further subdivided so one 'isa' link is exactly the same as any other 'isa' link.
B. All other relations are classified in an inheritance hierarchy. This is easy to see in syntax, where most linguists recognise that Object isa Complement, and that Complement isa Dependent. (See grammatical functions.) Outside language the hierarchical organisation of relations is clear in family structure, where Mother isa Parent and Parent isa Relative.
This treatment of relations is an important distinctive feature of WG, because it solves the problem of deciding what relations there are. If relations are all pre-defined by the theory, as most theories assume, their should be just a limited and universal set; and yet we seem to be able to learn an indefinite number of relations. (Think, for example, of 'ex', the relation between someone and another person to whom they used to be married.) WG explains how we do it: we can learn relation nodes in just the same way as we nodes other nodes.
This is an article from the Encyclopedia of Word Grammar and English grammar. If you refer to it, please give the url as "http://tinyurl.com/wg-encyc".