Not only have we to assume such an extent of forgetfulness and inaccuracy, about simple and striking facts of the immediate past, as is totally unexampled in any other range of experience. Not only have we to assume that distressing or exciting news about another person produces a havoc in the memory which has never been noted in connection with distress or excitement in any other form. We must leave this merely general ground, and make suppositions as detailed as the evidence itself. We must suppose that some people have a way of dating their letters in indifference to the calendar, or making entries in their diaries on the wrong page and never discovering the error; and that whole families have been struck by the collective hallucination that one of their members had made a particular remark, the substance of which had never entered that member's head; and that it is a recognised custom to write mournful letters about bereavements which have never occurred; and that when A describes to a friend how he has distinctly heard the voice of B, it is not infrequently by a slip of the tongue for C; and that when D says he is not subject to hallucinations of vision, it is through momentary forgetfulness of the fact that he has a spectral illusion once a week; and that when a wife interrupts her husband's slumbers with words of distress or alarm, it is only her fun, or a sudden morbid craving for undeserved sympathy; and that when people assert that they were in sound health, in good spirits, and wide awake, at a particular time which they had occasion to note, it is a safe conclusion that they were having a nightmare, or were the prostrate victims of nervous hypochondria.

Every one of these improbabilities is, perhaps, in itself a possibility; but as the narratives drive us from one desperate expedient to another, when time after time we are compelled to own that deliberate falsification is less unlikely than the assumptions we are making, and then again when we submit the theory of deliberate falsification to the cumulative test, and see what is involved in the supposition that hundreds of persons of established character, known to us for the most part and unknown to one another, have simultaneously formed a plot to deceive us - there comes a point where the reason rebels. Common sense persists in recognising that when phenomena, which are united by a fundamental characteristic and have every appearance of forming a single natural group, are presented to be explained, an explanation which multiplies causes is improbable, and an explanation which multiplies improbable causes becomes, at a certain point, incredible.

§ 18. I am aware that in its abstract form, and apart from actual study of the cases, this reasoning must be wholly unconvincing. But meanwhile the argument for the general trustworthiness of our evidence may be put in another and, perhaps, clearer light. Amid all their differences, the cases present one general characteristic - an unusual affection of one person, having no apparent relation to anything outside him except the unusual condition, otherwise unknown to him, of another person. It is this characteristic that gives them the appearance, as I have just said, of a true natural group. Now the full significance of these words may easily escape notice. They have an evidential as well as a theoretic bearing. They involve, of course, the hypothesis that the facts, if truly stated, are probably due to a single cause; but they involve, further, a very strong argument that the facts are truly stated. Let us suppose, for the moment, that any amount of laxity of memory and of statement may be expected even from first-hand witnesses, belonging to the educated class. And let us ignore all the heterogeneous improbabilities which we were just now considering; and assume that the mistakes mentioned, and others like them, may occur at any moment.

What, then, is the likelihood that all these various causes - all these errors of inference, lapses of memory, and exaggerations and perversions of narration - will issue in a consistent body of evidence, presenting one well-defined type of phenomenon, free in every case from excrescences or inconsistent features and explicable, and completely explicable, by one equally well-defined hypothesis? What is the likelihood that a number of narratives, which are assumed to have diverged in various ways from the actual facts, should thus converge to a single result? Several hundreds of independent and first-hand reporters have, wittingly or unwittingly, got loose from the truth, and are well started down the inclined plane of the marvellous. Yet all of them stop short at or within a given line - the line being the exact one up to which a particular explanation, not of theirs but of ours, can be extended, and beyond which it could not be extended. Tempting marvels lie further on - marvels which in the popular view are quite as likely to be true as the facts actually reported, and which the general traditions of the subject would connect with those facts. But our reporters one and all eschew them.

To take, for instance, the group of cases which the reader will probably find to be the most interesting, as it is also the largest, in our collection - apparitions at the time of death. Why should not such apparitions hold prolonged converse with the waking friend? Why should they not produce physical effects - shed tears on the pillow and make it wet, open the door and leave it open, or leave some tangible token of their presence? It is surely noteworthy that we have not had to reject, on grounds like these, a single narrative which on other grounds would have been admitted. Have all our informants drawn an arbitrary line, and all drawn precisely the same arbitrary line, between the mistakes and exaggerations of which they will be guilty, and the mistakes and exaggerations of which they will not? We might imagine them as travellers, ignorant of zoology, each of whom reports that he has landed on a strange shore, and has encountered a strange animal. Some of the travellers have been nearer the animal, and have had a better view of him than others, and their accounts vary in clearness; but these accounts, though independently drawn up, all point to the same source; they all present a consistent picture of the self-same animal, and, what is more, the picture is one which zoology can find no positive cause to distrust.