enunciate certain propositions in virtue of which the occurrence of some events can be inferred from the occurrence of other events. To these propositions we may give the name of 'causal laws.' Therefore, from the purely scientific point of view, we should go no further than the mere statement that such causal laws do subsist. This is evidently true, for if we take objective experience as it stands, there is simply the fact that certain sense-data are invariably followed by certain other sense-data. The sequence contains in itself neither hint as to the reason for this invariance, nor warrant that it will continue to hold in the future. Scientific observation alone, then, can do nothing more than formulate descriptions of these sequences, together with the statement that it seems probable that they will continue to hold in the future as they have invariably done in the past. From this point of view, any further extension of the principle of causality is both unnecessary and unjustifiable.
If the exponents of the scientific method were content to stop at this point all would be well; but they go further, and assert that the meaning of causality considered above is the only valid one. Yet the roots of the concept of causality go far deeper than this. If we trace the development of this concept during the growth of experience, we find that it is inseparably bound up with the notion of efficiency or activity. We ourselves, as active agents, initiate changes in our environment, and we realize our activity to be the ground of which these changes are the consequence. Many of the sequences which occur in experience independently of us, we can reproduce at will. Thus we arrive at the conception of efficient causality as distinct from merely descriptive causal laws, ourselves being efficient, and, for the most part, self-determined causes. Inevitably we come instinctively to consider efficient causality as the ground of those sequences which we observe in experience. Logically, as we have seen, mere observation only gives us the right to assert that certain sequences do recur, and to state the fact in a general proposition. Seeing, however, that we actually realize self-activity to be the ground of many sequences—sequences which we can always render essentially similar—there is no reason why
