terms to their object-matters, and their indirect symbolic references to other terms. Terms would not be elements of logic at all if they merely served, as they generally do serve, to call up vague mental images of the object-matters named. Ideas would not be elements of logic if they consisted in such images alone. Terms, with their involved ideas, enter into logic, because each implies, without actually stating, all the different judgments of which it habitually forms a subject or predicate.
Now although subject and predicate are constantly changing places in the course of ratiocinative argument, they are not essentially interchangeable. There are typical subjects which cannot become predicates, and typical predicates which cannot be properly treated as subjects. On the one hand, the names of particular persons, nations, places, and historical objects cannot stand as predicates, though they may stand as parts of predicates. On the other hand, certain verbal and adjectival predicates have, in order to become subjects for formal logical purposes, to be supplied with a concrete content, as when 'growing' becomes 'growing things'; but the essential meaning of such predicates is best expressed by abstract names, like 'growth.' Such abstract names form an artificial order of subjects; but they are really predicables (in a wider sense than the technical), being the generic class-names of certain predicates which occur naturally in verbal and adjectival forms and always belong to something else, as growth belongs to growing organisms or any other things which grow. Thus terms, and ideas as attached to terms, fall into two great groups.
These are concrete ideas, or the ideas of typical subjects (entities or quasi-entities) and abstract ideas, or the ideas of typical predicates (states, actions, qualities, relations, aspects—all of which may be called modes). The relation between concrete and abstract ideas is one of mutual subsumption from opposite standpoints. A particular quality, say rotundity, is only one among various qualities which belong to some type of entity, say an apple; but an entity such as an apple is only one among many entities resembling itself, and apples are only one class among many other classes of natural objects which agree
