§ 5. This last statement will possibly appear startling to the reader who is unacquainted with the history of metaphysical investigations into Causality. But it is easy to show that it is really the expression of an obvious truth. For the causal principle, as we have just seen, is an imperfect expression of the really axiomatic principle of Sufficient Reason or Ground and Consequence. And it is readily seen that the expression it gives to that principle, because imperfect, must be partially false. What the principle of Ground and Consequence says is, that the whole of existence is a single coherent system in which every part is determined by the nature of the whole as revealed in the complete system. But if this is true, each constituent of the system can only be completely determined by its connections with all the rest. No constituent can be entirely determined by its relations to a lesser part of the whole system, in the way presupposed by the notion of one-sided causal dependence. The “cause” must, if the principle of Ground and Consequence be valid, be determined by the “effect” no less than the “effect” by the “cause.” And therefore the causal postulate cannot be the whole truth. How this fatal logical defect in the principle of Causation makes itself felt in the logic of the inductive sciences, and how logicians have sought without success to avoid it, we shall incidentally see as our discussion proceeds. At present we must be content to note that, owing to this flaw, Causation, wherever it is asserted, can only be Appearance and never complete Reality, and that no science which works with the concepts of cause and effect can give us the highest truth. Of course, the logical defects of the concept need not impair its practical usefulness. Though it can never, for the reason given already, be ultimately true that any event is absolutely determined by antecedent events, the assumption may be sufficiently near the truth to yield useful deductions as to the course of occurrences, precisely as a mathematical approximation to the value of a surd quantity may, without being the exact truth, be close enough for practical use. Also, it might well be the case that the causal postulate approximates more nearly to the truth in some spheres of investigation than in others, a consideration which is not without its bearing on the ethical problems of freedom and responsibility.