They are all taken from the philosophic sciences—that is, the sciences dealing with phenomena which are partly determined by mind, and the systematic treatment of which is so similar that they are frequently studied in combination by a single thinker, and invariably so by the greatest thinkers of any. But were we to examine the history of the physical sciences, we should find that this method of wide comparison and rapid abstraction cannot, as Francis Bacon imagined, be successfully applied to them. The facts with which they deal are not transparent, not directly penetrable by thought; hence they must be treated deductively. Instead of a front attack, we must, so to speak, take them in the rear. Bacon never made a more unfortunate observation than when he said that the syllogism falls far short of the subtlety of Nature. Nature is even simpler than the syllogism, for she accomplishes her results by advancing from equation to equation. That which really does fall far short of her subtlety is precisely the Baconian induction with its superficial comparison of instances. No amount of observation could detect any resemblance between the bursting of a thunderstorm and the attraction of a loadstone, or between the burning of charcoal and the rusting a nail. But while philosophers cannot prescribe a method to physical science, they may, to a certain extent, bring it under their cognisance, by disengaging its fundamental conceptions and assumptions, and showing that they are functions of mind; by arranging the special sciences in systematic order for purposes of study; and by investigating the law of their historical evolution. Furthermore, since psychology is the central science of philosophy, and since it is closely connected with physiology, which in turn reposes on the inorganic sciences, a certain knowledge of the objective world is indispensable to any knowledge of ourselves. Lastly, since the subjective sphere not only rests, once for all, on the objective, but is also in a continual state of action and reaction with it, no philosophy can be complete which does not take into account the constitution of things as they exist independently of ourselves, in order to ascertain how far they are unalterable, and how far they may be modified to our advantage. We see, then, that Socrates, in restricting philosophy to human interests, was guided by a just tact; that in creating the method of dialectic abstraction, he created an instrument adequate to this investigation, but to this alone; and, finally, that human interests, understood in the largest sense, embrace a number of subsidiary studies which either did not exist when he taught, or which the inevitable superstitions of his age would not allow him to pursue.