Hume had written that “the justest and most plausible objection against a considerable part of metaphysics was that they are not properly a science, but arise either from the fruitless efforts of human vanity, which would penetrate into subjects utterly inaccessible to the human understanding, or from the craft of popular superstitions, which, being unable to defend themselves on fair ground, raise these entangling brambles to cover and protect them.”  In these considerations he found reason not for leaving superstition in possession of its ground, but for making a bold and arduous attack upon it in its haunts.  The great difficulty in the way of carrying the war into the enemy’s own camp was that in those days so-called science was itself cumbered with many illogical and metaphysical ideas, and for the first time in the present century the great advances of physical science, and, in particular, the renewed life poured by Darwin into the doctrine of evolution, made it possible to bring a new series of exact arguments against hazy metaphysical dogmas.  The militant side of agnosticism was directed against the camp of superstition and armed with the new weapons of exact science.  Its stern refusal of belief without adequate evidence was a challenge to all the supporters of the sanguine philosophy which replaces proof by assured and emphatic statement and restatement.  It is possible, although rare, for those who hold a positive belief upon evidence, howsoever insufficient, to leave their doubting neighbours in peace, and these neighbours, assured in their own beliefs, equally positive and perhaps equally unfounded, may return the lazy tolerance.  But the agnostic position is at once a reproof and a challenge to all who do not hold it.  Perhaps no one has ever put the agnostic attitude more clearly than Kant when he wrote that “the greatest and perhaps sole use of all philosophy of pure reason, is, after all, merely negative, since it serves, not as an organ on (for the enlargement of knowledge), but as a discipline for its delimitation:  and instead of discovering truth has only the modest merit of preventing error.”  It is precisely because it is addressed against error that agnosticism brings not peace but a sword; precisely because, instead of adding to the beliefs of the world, it seeks to examine them and perhaps by the examination to diminish them, that it aroused passionate resentment.  In this respect it stands entirely separate and apart from any other similar term, as all these implied a definite acceptance or rejection of some definite propositions.  Agnosticism means none of these things.  Huxley said of it: