We see, Haeckel's conception of substance changes like a chameleon before our very eyes. We are first told that there is a thing in itself, then that we do not know what it is, and finally that we do not even know that it is. We are naïvely told that the notion of substance will solve all riddles, make all things clear to us, then we are informed that it is a mystery, the greatest mystery of all, and finally it vanishes into thin air before our very gaze, and turns into a phantom which perhaps does not even exist. After making the conception of substance do service as a principle of explanation for 436 pages of his book, after having employed it as the support of real attributes, space, time and energy, Haeckel suddenly dismisses it as an utterly useless piece of metaphysical furniture.
But these are not the only inconsistencies in the doctrine of substance. We are told that substance is unknowable, that matter and force are its attributes. We are told that God, the thing in itself, is an intramundane being and acts in the substance as force or energy.[2] That is, the thing in itself is force. Yes, perhaps the original hypothetical chemical element, the prothyl, is the substance;[3] perhaps the world-ether is the creating god-head.[4] What does all this mean? The substance perhaps does not exist; the substance does exist, but is unknowable; the substance has real attributes, and we know them; the substance is energy; the substance is perhaps prothyl; the substance is perhaps the world-ether. Haeckel is certainly right in his remark that consistent thinking is a difficult business.
There is another point worth noting at this place which will come up again. Haeckel speaks of the mental aspect of the substance as mind, thought, sensation (Empfindung), energy, moving force. This is something like Schopenhauer's will, only that it is not a substance, but the attribute of a substance. As an attribute distinct from the
