them. Each is only what substance makes it, and cannot stand when substance withdraws itself and takes another shape.
The nature of substance, thus, may be summed up in three phases: the self identity of substance and the variety of the accidents; the immanence of substance in the accidents; the power of substance over the accidents.
We may now look at the defects of this conception when taken as a final category. Briefly, they spring from the fact that the unity of substance is abstract. The two aspects, universal and particular, have been brought within the compass of one thought, but they are still external to one another. Substance is the self-identity of the process, and although it exists only in the variety of the accidents, yet it does not include that variety as part of its own nature. The explanation which uses substance as its highest principle dissolves the particular in the universal; it traces the universal in the particular, but it does not take the universal concretely. If the conception of physical energy is used in such a way that it embodies this principle, then explanation will consist in tracing the identity of the quantity of energy in the consecutive forms; potential energy will be resolved into an equal quantity of kinetic energy, that into heat, and so on. The constant quantity of energy will be regarded as the reality, and thought will be satisfied when the quantitative identity is demonstrated.
The defects of this method of thinking are obvious, for no account is given of the transformation from the one mode to the next. The change of the accidents falls without substance; and when the accidents are resolved into substance their aspect of difference and variety is lost. The essence of the situation appears to be this. Substance is the all-pervading power in each accident and is the reality of each; but in referring an accident to substance we do not organize the accidents into a systematic whole, but merely dig within each for the hidden identity. We find, e.g., that the quantity of energy in question is present in the kinetic form and are satisfied; we do not trace the peculiar nature of the kinetic form back into potential energy and forward into heat. That is to say, we do not regard the differences as fundamental to substance, and so we explain each form not by its context