What we are ever doing in rational Discourse, what Knowledge constantly accomplishes, is to furnish an account, a reproduction of a series of operations. The World is a process--an activity. That was recognised as long ago as the days of Heracleitus, but his disciples did not--although we think there is good ground for believing that he did[60:1]--his disciples did not realise that a process, whilst it implies constant flux and change, implies also something permanent even in its mutations, something which undergoes the change and sustains the flow. To understand a thing is to discover how it _operates_. The eternal forms of things are laws of natural action. Such are the law of gravitation, the laws of optics or of chemical combination. A static picture unless so interpreted must be at once valueless and meaningless. It follows that Thought and Discourse, in furnishing us with Knowledge, must themselves be active, and must in some way or other reproduce the activity of Nature. Thought, in short, _is_ an Activity which reproduces the activity of things, the activity in which the phenomena of Nature arise. But how do we arrive at any apprehension of Natural Action? What informs us that Nature is a potency ever operative? What suggests to us the conception of potency at all? We reply that we arrive at the idea of potent action because we are ourselves active beings. Our organism maintains itself by constant physiological activities. These are the permanent constancies of transmutation which _constitute_ the organism. But superimposed upon these there are our voluntary exertional activities. By these latter we necessarily mingle with and indeed participate in the action of the natural forces which (as we usually say) surround us, but which in point of fact do more than surround us. The disparate grouping of natural bodies in vision blinds us to the fact that we are really not merely surrounded by but are mingled with and participate in the dynamic system.[61:1] We are continually pressing with our weight upon the bodies on which we rest, we are continually exerting or resisting the pressure of so-called adhering masses--resistance-points in one dynamic system of which we are ourselves a part. Thus it is that in our exertional action we reveal to our consciousness not only the forms of our own activity but the forms of the dynamic system which contains and yet transcends the Sensible and the Ideal. The theory we have suggested enables us to proceed at once to a rational explanation of Sensation. Sensation is _obstructed action_. A detailed consideration of as many as you like to take of the myriad constituents of our sensible Experience will continually and without exception confirm this simple fact.