What many people have not been able to forgive the generations of the Middle Ages, and especially the ecclesiastics of the centuries before our own, is that as educated men and leaders of the people they should have accepted the view that mental diseases may, in some of their forms at least, be due to possession by the devil or some other spiritual interference with the working of the human intellect. During the latter half of the nineteenth century, it became the custom among the educated to scoff at any possible manifestation of this kind. The interference of the spiritual world with any of man’s actions came to be looked upon as absurd, except by those who still clung to old-time beliefs and thought that new fashions in opinion might very well prove almost as variable as do corresponding fads in the realm of dress or of interests. The difficulty in the matter was that the generations of the latter nineteenth century lost their faith, to a great extent, in the existence of a spiritual world, and consequently it was easy to laugh at those who had found the interference of such a world as not only possible, but actual, in a great many affairs in human life. As a matter of fact, when we realize how many utterly inexplicable phenomena the earlier centuries tried to explain this way, it is not surprising to find their explanation sometimes wrong.
It is very easy, to my mind, for men of our generation to be too hard in their judgments of the men of the Middle Ages with regard to the curious phenomena, psychic, spiritistic and occult, which, with all our advance in science, are still almost as obscure to the eye of the intellect as they were seven centuries ago. The medieval generations saw a great many things that they could not explain happening round them, and attributed them to spiritual agencies. We have learned since that many of these things are merely natural, and must not be considered as due to anything else than the ordinary laws of nature. We have not eliminated belief in the spiritual world, however, and there is still a large proportion of mankind who think that they see, even in the matter-of-fact world around them of the present day, many signs of interference in human affairs by agencies distinct from those of human beings and quite independent of matter. It is easy to dismiss this side of the question with a shrug of the shoulders and say that it need not be taken into account. A man who does this easily succeeds in convincing himself that there are no evidences for spiritual manifestations in our life, and that the stories with regard to them are all nonsense.
It is curious, however, that anyone who investigates and does not merely dismiss at once, is very prone to come to a contrary conclusion, even though all his training and the traditions of his education are opposed to such an admission. There are many prominent scientists who have allowed themselves to be drawn into the investigation of spiritualistic manifestations so-called. Very few of them have come away from their investigations entirely convinced that there was nothing in them. Frauds they have found; sleight-of-hand impositions they have exposed; but apart from all these, there is a residue of phenomena which they cannot explain and which convinces many of them of the existence and the mundane action of forces independent of matter. The men who come to these conclusions are not only the ignorant, nor the over-credulous, but frequently representative leaders in scientific thought–men who are known to be thoroughly capable of weighing evidence, prominent lawyers and judges, above all, men who are accustomed to investigation as most painstaking scientists and faithful students of nature.
James J. Walsh, The Popes and Science (1908)