§ 1. The fourth of the features which characterise the pre-scientific view of the world we found to be the belief that things act and are acted upon by one another. The problems to which this belief gives rise are so vast, and have been historically of such significance for Metaphysics, that they will require a separate chapter for their discussion. In the conception of the interaction of things as it exists for the naïve pre-scientific mind, we may distinguish at least two aspects. There is (1) the belief that things _change_, that within the unity of the one thing there is a succession of different states; and (2) the belief that the changes of state of various things are so inter-connected that the changes in one thing serve as occasions for definite changes in other things. We thus have to discuss, first, the general notion of change as an inseparable aspect of the being of things, and next the concept of systematic inter-connection between the changes of state of different things. (_a_) _Change._ The problem presented by the apparently unceasing mutability of existence is one of the earliest as well as one of the most persistent in the whole range of Philosophy. In itself it might seem that the successive presentation in time of various states is neither more nor less noteworthy a feature of the world of experience than the simultaneous presentation of a like variety, but the problem of mutability has always appealed with special force to the human imagination from its intimate connection with our personal hopes and fears, ambitions and disappointments. Tempora mutantur, _nos_ et mutamur in illis; there is the secret of the persistence with which our philosophic thought has from the first revolved round this special problem. There, too, we may find a pregnant hint of the central paradox implied in all mutability—namely, that only the identical and permanent can change. It is because the self which changes with the flux of time and circumstance is still in some measure the same old self that we feel its changes to be so replete with matter for exultation and despair. Were we completely new-made with each successive change in our self, there would no longer be ground for joy in transition to the better or grief at alteration for the worse.