It escapes attention in much of the contemporary logic of transitive and non-transitive, symmetrical and non-symmetrical relations, because the terms are so loaded that there are no propositions at all, but only discriminations of orders of terms. The terms which figure in the discussions, in other words, are correlatives--"brother," "parent," "up," "to the right of," "like," "greater," "after." Such terms are not logical terms; they are _halves_ of such terms as "brother-other-offspring-of-the-same-parents"; "parent-child"; "up-down"; "right-left"; "thing-similar-to-another-thing"; "greater-less"; "after-before." They express positions in a _determined_ situation; they are _relatives_, not relations. They lack implications, being explicit. But a man who is a brother and also a rival in love, and a poorer man than his rival brother, expresses an interaction of different terms from which something might happen: terms with implications, terms constituting a proposition, which a correlative term never does--till brought into conjunction with a term of which it is not a relative. To have called a thing "up" or "brother" is to have already solved its import in some situation. It is dead till set to work in some _other_ situation. Experience shows, moreover, that certain qualities of things are much more fruitful and much more controllable than others when taken as meanings to be used in drawing conclusions. The term must be of a nature to develop a method of behavior by which to test whether it is the meaning of the situation. Since it is desirable to have a stock of meanings on hand which are so connected that we can move readily from one to another in any direction, the stock is effective in just the degree in which it has been worked into a system--a comprehensive and orderly arrangement. Hence, while all meanings are derived from things which antedate suggestion--or thinking or "consciousness"--not all qualities are equally fitted to be meanings of a wide efficiency, and it is a work of art to select the proper qualities for doing the work. This corresponds to the working over of raw material into an effective tool. A spade or a watchspring is made out of antecedent material, but does not pre-exist as a ready-made tool; and, the more delicate and complicated the work which it has to do, the more art intervenes. These summary remarks will have to pass muster as indicating what a more extensive treatment of a mathematical system of terms would show. Man began by working such qualities as hate and love and fear and beauty into the meanings by which to interpret and control the perplexities of life. When they demonstrated their inefficacy, he had recourse to such qualities as heavy and light, wet and dry, making them into natural essences or explanatory and regulatory meanings. That Greek mediaeval science did not get very far on these lines is a commonplace. Scientific progress and practical control as systematic