The first stage of the development closes with attempts on all hands to put the results in an encyclopædiacal form. Humboldt’s Cosmos is a good example of this tendency, manifested so widely. Matter, masses, and _functions_ are the subjects of investigation. Reflection investigates _functions_ and seizes the abstract category of force, and straightway we are in the second stage. Matter, as such, loses its interest, and “correlation of forces” absorbs all attention. Force is an arrogant category and will not be co-ordinated with matter; if admitted, we are led to a pure dynamism. This will become evident as follows: I. Force implies confinement (to give it direction); it demands, likewise, an “occasion,” or soliciting force to call it into activity. II. But it cannot be confined except by force; its occasion must be a force likewise. III. Thus, since its confinement and “occasion” are forces, force can only act upon forces—upon matter only in so far as that is a force. Its nature requires confinement in order to manifest it, and hence it cannot act or exist except in unity with other forces which likewise have the same dependence upon it that it has upon them. _Hence a force has no independent subsistence, but is only an element of a combination of opposed forces_, which combination is a unity existing in an opposed manner (or composed of forces in a state of tension). This deeper unity which we come upon as the ground of force is properly named _law_. From this, two corollaries are to be drawn: (1.) That matter is merely a name for various forces, as resistance, attraction and repulsion, etc. (2.) That force is no ultimate category, but, upon reflection, is seen to rest upon law as a deeper category (not law as a mere similarity of phenomena, but as a true unity underlying phenomenal multiplicity). From the nature of the category of force we see that whoever adopts it as the ultimate, embarks on an ocean of dualism, and instead of “seeing everywhere the one and all” as did Xenophanes, he will see everywhere the self opposed, the contradictory. The crisis which science has now reached is of this nature. The second stage is at its commencement with the great bulk of scientific men. To illustrate the self-nugatory character ascribed to this stage we shall adduce some of the most prominent positions of Herbert Spencer, whom we regard as the ablest exponent of this movement. These contradictions are not to be deprecated, as though they indicated a decline of thought; on the contrary, they show an increased activity, (though in the stage of mere reflection,) and give us good omens for the future. The era of stupid mechanical thinkers is over, and we have entered upon the active, _chemical_ stage of thought, wherein the thinker is trained to consciousness concerning his abstract categories, which, as Hegel says, “drive him around in their whirling circle.”