If we ask how the causal postulate, being as it must be only imperfectly true, comes to be made, the answer is obvious. The whole conception is anthropomorphic in origin, and owes its existence to our practical needs. To take the latter point first, logically there is no better reason for treating an event as determined solely by antecedents, than for treating it as solely determined by subsequent events. Yet when the latter supposition is made, as it is by all believers in omens and presages, we all agree to condemn it as superstitious. Why is this? Two reasons may be assigned. (_a_) Even granting that an event may be determined by subsequent events, yet, as _we_ do not know what these events are until after their occurrence, we should have no means of inferring by _what_ particular events yet to come any present event was conditioned, and thus should be thrown back upon mere unprincipled guess-work if we attempted to assign its, as yet future, conditions. (_b_) A more important consideration is that our search for causes is ultimately derived from the search for _means_ to the practical realisation of results in which we are interested. We desire to know the conditions of occurrences primarily, in order to produce those occurrences for ourselves by setting up their conditions. It is therefore essential to us for our practical purposes to seek the conditions of an occurrence exclusively among its antecedents, and the causal postulate which asserts that the complete conditions of the event are comprised somewhere in the series of antecedent events is thus the intellectual expression of the demand made by our practical needs upon Reality. We postulate it because, unless the postulate is approximately realised, we cannot intervene with success in the course of events. We refuse, except as a pure speculation, to entertain the notion that an event may be determined by subsequent as well as by antecedent events, because that notion leads to no practical rules for operation upon our environment.