There is, however, one precaution which must be observed, and without which the whole of the system just described is as uncertain and conditional as the rest of science. Before we can argue from what is to what has been, we must first know for certain what is. Before we can conclude that a patient has been healed by faith or cured miraculously of an incurable complaint, we must first have medical evidence to show that he had the disease. Or, to take a better and closer illustration from medicine, it is premature to assign a cause for a patient's condition before his condition has been diagnosed; and physicians who differ in their diagnosis will naturally differ as to the causes in the patient's past history which are responsible for his state. If, then, the evolutionist is to attain accuracy in his description of the process by which the totality of things has come to be what it is, he must first know what it is. Before we can trace the evolution of morality, for instance, we must make up our minds as to what it is. If we regard it as an illusion, we shall hold that it is subject to the same laws as other illusions, and we shall have no difficulty in showing that its evolution was a necessary consequence of those laws. Or, again, if we hold that religion is mere foolery or hysteria, we shall naturally infer a very different process for its evolution than if we feel it to be a permanent manifestation of the common consciousness in the same sense that morality is. A distinguished German mythologist, starting from the former diagnosis, has no difficulty in evolving primitive religion out of primitive drunkenness. In fine, if we regard "what is" as giving the data by which we are to determine what has been, it is clear that to understand what has been we must properly appreciate what is. This is in accordance with the conclusion which we have reached previously that it is only by studying its effects that we can properly understand a cause. To judge a thing properly we must know the effects it is capable of producing: to know what a thing is we must observe what it becomes or what it is capable of becoming at its best. We cannot judge the value of the moral character or the moral ideal fairly if we take a low specimen to go by; nor if we knew nothing more of morality than what we could observe of its rudiments in the higher animals, should we know much about it. It is by its highest manifestations that we most correctly judge either morality or art, and it is only through them that we can be properly said even to understand what either art or morality is. So, too, taking the religious ideal as love of God and man, we must judge religion not by its imperfect manifestations in imperfect beings, but by its perfect revelation and realisation in Christ.