Meanwhile, she asks nothing at all about the first cause of phenomena, so long as she has so many more proximate causes to investigate. Many of the most eminent men of science go so far, indeed, as to assert that the first cause will never become the object of scientific investigation, and call it, with Herbert Spencer, ‘the Unknowable,’ or exclaim despondingly with Du Bois-Reymond, _Ignorabimus_. Both of them in this respect are completely unscientific, and only prove that even clear thinkers like Spencer, and sober investigators like Du Bois-Reymond, stand yet under the influence of theological dreams. Science can speak of no Unknowable, since this would presuppose that she is able to mark exactly the boundaries of the Knowable. This, however, she cannot do, since every new discovery thrusts back that boundary. Moreover, the acceptance of an Unknowable involves the acknowledgment that there is something which we cannot know. Now, in order to be able seriously to assert the existence of this Something, either we must have acquired some knowledge of it, however slight and indistinct, and this, therefore, would prove that it cannot be unknowable, since we actually know it, and nothing then would justify us in declaring beforehand that our present knowledge of it, however little it may be, will not be extended and deepened; or else we have no knowledge, even of the minutest character, of the philosopher’s Unknowable, in which case it cannot exist for us. The whole conception is based upon nothing, and the word is an idle creation of a dreaming imagination. The same thing can be said of _Ignorabimus_. It is the opposite of science. It is not a correct inference from well-founded premises, it is not the result of observation, but a mystical prophecy. No one has the right to make communications with respect to the future as matters of fact. Science can announce what she knows to-day; she can also mark off exactly what she does not know; but to say what she will or will not at any time know is not her office.