Abstraction: Nature, . . .

It is argued that abstract cognitive processes entail the processing of relations, which differ from more primitive cognitive processes in being more accessible, more flexible, and less content-specific. A relation is a binding between a relation-symbol or predicate, and one or more arguments. Each argument corresponds to a slot which can be filled in a number of ways, so the relation is independent of specific arguments. The binding of arguments to a relationsymbol means that the relation can be an argument to other relations, and is therefore accessible to other cognitive processes based on relations. It can be shown that the building blocks of cognitive processes, such as propositions, and trees can be expressed as relations. Each argument constitutes a dimension in the space represented by the relation, and the number of arguments provides a metric for conceptual complexity. Neural net modelling shows why relational representations impose a processing load which is a function of the number of dimensions