Throughout the foregoing essays, therefore, I have assumed that all forms of energy are but relatively varying expressions of the same fact--the fact, namely, which Mr. Spencer means to express when he says that force is persistent. And it seems to me almost needless to show that this fact is really the basis of all science. For unless this fact is assumed as a postulate, not only would scientific inquiry become impossible, but all experience would become chaotic. The physicist could not prosecute his researches unless he presupposed that the forces which he measures are of a permanent nature, any more than could the chemist prosecute his researches unless he presupposed that the materials which he estimates by energy-units are likewise of a permanent nature. And similarly with all the other sciences, as well as with every judgment in our daily experience. If, therefore, any one should be hypercritical enough to dispute the position that the doctrine of the conservation of energy constitutes the "ultimate datum" of science, I think it will be enough to observe that if this is _not_ the "ultimate datum" of science, science can have no "ultimate datum" at all. For any datum more ultimate than permanent existence is manifestly impossible, while any such datum as non-permanent existence would clearly render science impossible. Even, therefore, if such hypercriticism had a valid basis of apparently adverse fact whereon to stand, I should feel myself justified in neglecting it on _a priori_ grounds; but the only basis on which such hypercriticism can rest is, not the knowledge of any adverse facts, but the ignorance of certain facts which we must either conclude to be facts or else conclude that science can have no ultimate datum whereon to rest. In the foregoing essays, therefore, I have not scrupled to maintain that the ultimate datum of science is destructive of teleology as a scientific argument for Theism; because, unless we deny the possibility of any such ultimate datum, and so land ourselves in hopeless scepticism, we must conclude that there can be no datum more ultimate than this--Permanent Existence; and this is just the datum which we have seen to be destructive of teleology as a scientific argument for Theism.