The means whereby this work of Nature is brought to its consummate issue are forces of Nature working under her Laws by the method of cause and effect. The principle, or “law,” of causation is a metaphysical postulate; in the sense that such a fact as causation is unproved and unprovable. No man has ever observed a case of causation, as is a commonplace with the latterday psychologists. But such a doubt does not present itself seriously in the days of handicraft; it would be out of touch with the spirit of the time and the discipline of that craftsmanship out of which the spirit of the time arises. To the inquiring minds of that era it is a matter of course and of common sense that the forces of Nature are seen to work out the effects which emerge before their eyes. What they see in fact may be, as the modern psychologists would perhaps say, a certain concomitance and sequence in the observed phenomena; but what those observers see in effect is always a certain cause working out a certain effect. The imputation of causal efficiency to the observed phenomena is so thoroughly a matter of course that there is no sense of imputation in the observer’s mind. Observation simply, without imputation of anthropomorphic qualities and efficacies, should yield nothing more to the purpose than idle concomitance and sequence of phenomena, but there is, in effect, none of this early scientific work done in terms of simple concomitance or sequence alone; nor for that matter, has any of the effective (theoretical) work of modern science been carried to an issue by the use of such objective terms of concomitance and sequence alone, whether in that or in a later age, without the help of a putative causal nexus. Through the early modern scientific period there runs an increasingly free and frequent recourse to statistical argument,--in the material sciences a recourse to punctilious measurement, enumeration and instruments of precision; but it is of the essence of the case that the phenomenal facts which so are subjected to measurement and statistical computation are facts selected for the purpose on the strength of their (putatively) known causal implication in the problem whose solution is sought, and that the facts which emerge from these measurements, computations, and instruments of precision, are turned to account in an argument of cause and effect; they have served their purpose only when and in so far as they enable the inquirer to determine the course of efficient transition from a putative cause to a putative effect, or conversely.