different relational fields—a fact of which Spencer took too little cognizance, so bent was he on some sort of unification at all hazards. Revert now to a field of gravitative relatedness, in which the motion of things is the kind of change, while the rate of change is expressible in a formula; may we not say that the co-presence of things in this relationship does imply certain motions and changes of motion within the system to which the term gravitative applies? There seems little room for ambiguity if we call what is thus implied the effect, and if we term those modes of relatedness which carry this kind of implication, effective. It may, however, be said that it sounds somewhat strange to speak of relations as effective. How can mere relatedness as such do anything? What is implied by the effect is surely, it will be urged, a cause in the full and rich sense of the word—a cause which produces the effect. For what is here suggested is nothing more than a generalized statement of the truth that the relational constitution of the system being what it is, the changes are what they are! And so we come back to the conception of an agency which in some way produces the observable change—of a power which is active behind the phenomenal scene—of force and cause in the Spencerian sense. But, so far as scientific interpretation is concerned, this reference to Source—for such it really is—is useless. The gravitative system can be dealt with scientifically just as well without it as with it.

What, then, becomes of the scientific conception of energy? Is not energy that which produces observable change? Is it not active in the sense required? And can we say that this conception is useless for scientific interpretation? I suppose most of us, in our student days, have passed through the phase of regarding energy as an active demon which plays a notorious part in the physical drama. Spencer loved it dearly. But some of us, under what we consider wiser guidance, hold that what we should understand by kinetic energy is nothing of this sort. It is a constant ratio of variables, conveniently expressed as 1/2mv². That, however, it may be said, is absurd. Energy is not merely a ratio or a formula; it is something much more real; perhaps the most real of all the realities the being of which has been disclosed by physical science. Granted in a sense, and a very true sense. But what is this reality? It is the reality of the changes themselves in those fields of relatedness to which the formula has reference. There is nothing, I conceive, in the modern treatment of energy that affords any scientific justification of the Spencerian view[43] that energy is an agent through the activity of which the constant ratio of variables is maintained in the physical world.

I feel sure that it will still be said that change must inevitably imply that which produces change, and that, even if energy be only a ratio of variables within a changing field, there is still the implication of Force as the real Cause of which the change itself, however formulated, is the effect. No doubt this is one of the meanings which the ambiguous words force and cause may carry. It is to remove this ambiguity that I have suggested that the word Source should be substituted for cause in this sense. And what about force? In one of its meanings it now generally stands for a measure of change. For those who accept Source as a scientific concept it may well stand for the measure or degree of its activity gauged by the phenomenal effect; for those who do not accept it, the measure or degree of the change itself[44]—to be dealt with in mechanics in terms of mass and acceleration. This leaves outstanding, however, the use of the word force in the phrase—the forces of nature—gravitative force, cohesive force, electromotive force, and so on. It was, I take it, with this usage in view that Spencer spoke of vital, mental, and social forces. Now the reference in each of these cases is to some specific mode of relatedness among the things concerned. We need to name it in some way; and this is the way that is, rather unfortunately, sanctioned by custom and long usage. When we say that a thing is in a field of electromotive force we mean (do we not?) that the relatedness is of that particular kind named electromotive, and not of another kind. When Spencer spoke of social forces he had in view changes which take place within a field of social relationships. We do not really need the word force in this sense, since the term relatedness would suffice, and has no misleading associations. But there it is: our business should be to understand clearly what it means. It does not, or should not, I think, mean more, in this connexion, than a particular kind of relatedness in virtue of which an observable kind of change occurs.

We may now pass to cause and conditions. When Spencer distinguishes between those conspicuous antecedents which we call the causes and those accompanying antecedents which we call the conditions, he invites the question: What, then, is the essential difference between them? If the accompanying antecedents are distinguished as inconspicuous, we surely need some criterion of the distinction. Furthermore, inconspicuous conditions are, in science, every whit as important as those which are conspicuous. Now we all know that Mill regarded the cause as 'the sum total of the conditions positive and negative taken together.'[45] But he expressly distinguishes between events and states.[46] Discussing, for example, the case of a man who eats of a particular dish and dies in consequence, he says:

'The various conditions, except the single one of eating the food, were not events but states possessing more or less of permanency, and might therefore have preceded the effect by an indefinite length of duration, for want of that event which was requisite to complete the required concurrence of conditions.'

Again he says:

'When sulphur, charcoal, and nitre are put together in certain proportions and in a certain manner, the effect is, not an explosion, but that the mixture acquires a property by which in given circumstances it will explode. The ingredients of the gunpowder have been brought into a state of preparedness for exploding as soon as the other conditions of an explosion shall have occurred.'

And he tells us that physiological processes 'often have for the chief part of their operation to predispose the constitution to some mode of action'.

This distinction may profitably be carried further and emphasized in our terminology. Take any thing, or any integrated group of things, regarded as that higher order of thing which we call a self-contained system. Process occurs therein, and process involves change. In so far as the system is self-contained its changes and states are inherent in its constitution. We need a term by which to designate that which is thus inherent and constitutional. The term ground might be reserved for this purpose. The word ground has its natural home in logic. It