It is, of course, obvious that the principle of Causation as thus understood is not a necessary logical deduction from the principle of Ground and Consequence. It might be the case that all occurrences form a coherent plan or system, such that if you once grasped the principle of the system you could infer from it what precise occurrence must take place at any one moment, and yet it might be impossible to discover this principle by an examination of the course of events up to the present moment. In other words, the principle of the systematic interconnection of events might be valid, and yet the events of the present might depend on those which will succeed them in the future no less than on those which have preceded them in the past. In that case it would be impossible with absolute logical certainty to infer what will occur at a given moment from the mere examination of what has preceded, _i.e._ the principle of Causation as used in the sciences would not be logically valid.[104] Cause, as currently understood, is thus identical not with the whole true logical ground, but with the ground so far as it can be discovered in the train of temporally antecedent circumstances, _i.e._ cause is _incomplete_ ground. This point is important, as it shows that the principle of Causation is not, like the principle of Sufficient Reason, axiomatic. It is no necessary logical consequence of the knowability or systematic character of the Real that an event should be completely determined by temporally antecedent events; for anything that is implied in the systematic character of the Real, the event may be equally dependent on subsequent occurrences. Again, the principle of Causation cannot be empirically established by an appeal to the actual course of experience. Actual experience is certainly not sufficient to show that every event is absolutely determined by its antecedent conditions; at most the success of our scientific hypotheses based upon the assumption of causality only avails to show that events may be inferred from their antecedents with sufficient accuracy to make the causal assumption practically useful. Regarded as a universal principle of scientific procedure, the causal assumption must be pronounced to be neither an axiom nor an empirical truth but a _postulate_, in the strict sense of the word, _i.e._ an assumption which cannot be logically justified, but is made because of its practical value, and depends upon the success with which it can be applied for confirmation. In the sense that it is a postulate which experience may confirm but cannot prove, it may properly be said to be _a priori_, but it is manifestly not _a priori_ in the more familiar Kantian sense of the word. That is, it is not a necessary and indispensable axiom without which systematic knowledge would be impossible. For, as we have already seen and shall see more fully in the immediate sequel, it may not be, and indeed in the last resort cannot be, true.