If the methods of science are reliable, (and they have been justified by their brilliant success,) we have indeed a criterion for the interpretation of facts; and this criterion for the interpretation of facts, no less than the criterion of single observations is based upon monism. If the world is really a universe, if there is oneness in the All, if there is a unity of law throughout nature, our interpretations of the different facts must agree among themselves. They cannot and should not contradict one another; and whenever they do, it is a certain sign that somewhere there is something wrong in our interpretation of facts. Philosophy has ceased to be a metaphysical world-theory. The interpretation of facts no longer means a hypothetical assumption which will square all the irregularities among facts that we are unable to account for, but simply a methodical systematisation of facts, enabling us to recognise the sameness of law in the irregularities apparent in innumerable individual instances. Interpretation in this sense means harmonisation; it means an orderly arrangement; classification with due discrimination. An explanation of natural phenomena is not the carrying of an hypothesis in to facts out of the realms of our imagination, out of depths unknown, by what might be styled revelation or inspiration, but it is a comparison of facts with facts. The hypothesis we apply to facts must come from facts and must cover facts. That element in an hypothesis which does not cover facts is redundant as an explanation; it is useless as such, or even dangerous; and unless it serves as an aid to thought where ignorance of facts requires some assistance, some allegorical symbol, some auxiliary construction,—unless it is to the scientist what crutches are to the lame,—it must be dropped. Accordingly, the criterion of truth is the perfect agreement of all facts, of all interpretations and explanations of facts among themselves. If two facts (such as we conceive them) do not agree with each other, we must revise them; and it may be stated as a matter of experience, that our mind will find no peace until a monistic conception is reached. A monistic conception is the perfect agreement of all facts in a methodical system, so that the same law is recognised to prevail in all instances, and the most different events are conceived as acting under different conditions yet in accord with the same law. * * * * *