The law of Causality is the most important law of thought, after that of Identity. Reason and result are often confused with cause and effect. The reason on account of which we do a thing is not, however, the cause by which it occurs. The cause is the complexity of all conditions which make it possible, and the reason of its performance coincides with a conscious design on our part that constitutes our purpose. Causality has nothing in common with the concept of purpose. The principal of Sufficient Reason has been made the bridge between Causality and Design. Probably human experience reached first the conception that nothing occurs without sufficient reason, and only later, by a further mental step, the conviction that everything for which the necessary conditions exist takes place. With this conviction, the concept of causality became clear; but, at the same time the bridge which connects it with the theory of design in the succession of events was destroyed, so that only a logical leap can restore us to this incomplete conception of earlier experience. Causal necessity excludes purposed necessity. That which takes place may be regarded as, in one direction, conformable to an end, but may, on the other hand, conform to no end in any direction. A succession of events conforms to purpose only in so far as it is regarded by a particular consciousness which combines it in thought with ends of its own or such as it ascribes to another consciousness. In the law of Causality, as in the law of Identity, the necessity of self-consistency and the self-consistency of Necessity reaches expression. The sufficient reason is simply the completeness of the conditions, with the existence of which the event takes place, and the absence of which the event fails to take place. Spinoza's "Will and intellect are one and the same" is the ethical law of Identity. All thought is willed; that is, indivisible from a certain coloring which it has in virtue of its identity with the will, just as all will is connected with thought; there is, indeed, a will-less thought, which might, however, just as correctly be called "unthinking thought,"[74] just as "unthinking willing" is, in reality, will-less willing. In all mental operations, the identity of the two functions is found. A will is unthinkable without something willed--an end, given by thought. It is the fact that, in his practical life, man recognizes purpose as a necessity, which causes him to read purpose into nature.