be able to give it – must always just as necessarily be tainted with two imperfections (as it were with two sores, or like Achilles with the vulnerable heel, or the devil with the horse's hoof), on account of which everything so explained really remains still unexplained. First with this imperfection, that the beginning of every explanatory chain of causes and effects, i.e., of connected changes, can absolutely never be reached, but, just like the limits of the world in space and time, unceasingly recedes in infinito. Secondly with this, that the whole of the efficient causes out of which everything is explained constantly rest upon something which is completely inexplicable, the original qualities of things and the natural forces which play a prominent part among them, by virtue of which they produce a specific kind of effect, e.g., weight, hardness, impulsive force, elasticity, warmth, electricity, chemical forces &c., and which now remain in every explanation which is given, like an unknown quantity, which absolutely cannot be eliminated, in an otherwise perfectly solved algebraical equation. Accordingly there is no fragment of clay, however little worth, that is not entirely composed of inexplicable qualities. Thus these two inevitable defects in every purely physical, i.e., causal, explanation show that such an explanation can only be relative, and that its whole method and nature cannot be the only one, the ultimate and thus the sufficient one, i.e., cannot be the method of explanation that can ever lead to the satisfactory solution of the difficult riddle of things, and to the true understanding of the world and existence; but that the physical explanation in general and as such requires further a metaphysical explanation, which affords us the key to all its assumptions, but just on this account must necessarily follow quite a different path. The first step to this is that one should bring to distinct consciousness and firmly retain the difference of the two, hence the difference between physics and metaphysics. It rests in general on the Kantian distinction between phenomenon
