Page:Philosophical Review Volume 19.djvu/260

246 In every attempt at proof we are bound to include some form of the same ideas as an assumption. Though it remains to modern science to define exactly what are the permanent elements in the constitution of physical existence, to separate essential from accidental accompaniments, yet the final result, whatever it may be, is but the clearer mental presentation of ideas which are implicit in the foundation of human thought. Their negation is inconceivable. They possess that highest possible criterion of truth that, when once the relations are disentangled, and clearly represented in thought, their opposite requires the impossible assumption that something has become nothing.

This discussion supplies the best opportunity for answering another question that has often been raised concerning this principle and concerning Spencer's formula of evolution. Doubt has sometimes been expressed whether these ideas are physical or metaphysical, and, if the former, what is their relation to Spencer's particular system of metaphysics, as expressed in "The Unknowable." To the first question there is only one possible answer. The formula of evolution and the principle of the persistence of force are purely physical. Their truth or falsehood is entirely independent of Spencer's metaphysics. This statement should require small emphasis. An objective philosophy, concerned with the unification of positive knowledge, must be judged by its congruity with the facts it seeks to coordinate and explain, and cannot be dependent on metaphysical principles. That Spencer recognized and asserted this essential separation is shown by the following passage: "The subjects on which we are about to enter (The Knowable) are independent of the subjects thus far discussed (The Unknowable) and he may reject any or all of that which has gone before while leaving himself free to accept any or all of that which is now to come. ...

"But an account of the Transformation of Things, given in