The law of the conservation of matter and energy is nothing but an application of the principle of identity to nature as a whole. And the law of cause and effect is again a corollary only of the law of the conservation of matter and energy. The law of causation is a formula which maintains that there is identity in difference. Some motion produces a change of form. There is accordingly a different state after the motion than before. Yet the total amount of matter and energy remains the same. This is the identity in the change. David Hume and with him John Stuart Mill and the empiricists misunderstood the problem of causation. Instead of considering cause and effect as one continuous process that should be analysed, they considered cause and effect separately and attempted a synthesis. In addition to this mistake, causes as well as effects were defined to be objects. Hume says cause and effect are objects following one another. Cause however is a process; it is a motion, a change that takes place, an event that happens; it is not a thing. And effect is the product of such a process. Effect is a special form, a special state of things, a special configuration, but not the material of which this configuration consists. A certain poison introduced into the stomach of a living being produces certain motions in the bowels, called cramps, which may finally prove fatal. One change produces other changes and their product is a new state of things which is accompanied with pain and ends in death. It is wrong to call strychnine the cause and a dead mouse the effect. But if we call strychnine the cause and a dead mouse the effect, we must forever despair of solving the problem of causation by a reduction to the principle of identity, for strychnine is not at all identical with a dead mouse. No cause is the same thing as its effect, and we can by no means identify cause and effect. And yet the principle of identity holds good. The identity in causation is the conservation of matter and energy in a change of form.