The principle that “Reality is not self-contradictory” at first sight might appear to be merely negative; we might object that it only tells us what reality is _not_, and still leaves us quite in the dark as to what it _is_. This would, however, be a serious misconception. As we learn from modern scientific Logic, no true and significant negative judgment is merely negative; all significant negation is really exclusion resting upon a positive basis. I can never, that is, truly declare that _A is not B_, except on the strength of some piece of positive knowledge which is inconsistent with, or excludes, the possibility of A being B.[10] My own ignorance or failure to find sufficient ground for the assertion _A is B_ is never of itself logical warrant for the judgment _A is not B_; that _A is not B_ I can never truly assert, except on the ground of some other truth which would be contradicted if A were affirmed to be B. Hence to say “Reality is not self-contradictory” is as much as to say that we have true and certain knowledge that reality is positively self-consistent or coherent; that is to say that, whatever else it may be, it is at least a systematic whole of some kind or other. How much further our knowledge about reality goes, what kind of a whole we can certainly know it to be, it will be the business of succeeding portions of this work to discuss; but even at the present stage of the inquiry we can confidently say that unless the distinction between the real and the apparent is purely meaningless, it is positively certain that Reality,[11] or the universe, is a self-consistent systematic whole.