(2) These difficulties, in a more or less clearly apprehended form, have led many recent writers on inductive Logic to modify the definition which was still satisfactory to Mill. Cause and effect, we are now told, are not distinct events, but earlier and later stages in a continuous process. The real business of science is not to discover “laws of connection” between distinct events or “phenomena,” but to invent general mathematical formulae by the aid of which we may trace the course of continuous processes. The discovery of causes, from this point of view, is reduced to the construction of formulæ which exhibit some quantity as a function of a time-variable. Fully worked out, this view of the nature of experimental science leads to the so-called “descriptive” ideal of scientific explanation, advocated by such eminent thinkers as Kirchhoff, Mach, and Ostwald among physicists, and, with various modifications, Avenarius, Münsterberg, Royce, and James Ward among recent philosophers. According to this doctrine, the ultimate ideal of science, or at any rate of physical science, is simply the description of the course of events by the aid of the fewest and simplest general formulæ. _Why_ things happen as they do, it is now said, is no proper question for science; its sole business is to enable us to calculate _how_ they will happen. With the general epistemological questions raised by this doctrine we must deal later in our third and fourth books. At present we are concerned only with its bearing on the notion of Causal Relation.[107] The important point for our immediate purpose is that the reduction of all events to continuous processes really does away with Causation altogether, as is recognised by those adherents of the theory who openly propose to expel the word “cause” from the language of science.[108] For in a continuous process it is purely arbitrary where we shall mentally draw the dividing line which is to mark the boundary between the “earlier” and the “later” stage. What the descriptive formula, with the aid of which we trace the course of the process by giving a series of successive values to our time-variable presents, is not the “cause” of the process but the “law” of it. Instead of looking upon the later stages of the process as determined by the earlier, we are now looking upon the process as a whole as the expression in detail of a single principle. We have, in fact, abandoned the category of cause and effect for that of Ground and Consequence. We are seeking the ground of the whole process not in a set of temporally preceding events, but in its own pervading principle.