To my surprise, this statement of what, after the closest reflection, I still conceive to be the right conclusion, has been hailed as a satisfactory admission by opponents, and lamented as a perilous concession by sympathisers.  Indeed, the tone of the comments of some candid friends has been such that I began to suspect that I must be entering upon a process of retrogressive metamorphosis which might eventually give me a place among the respectabilities.  The prospect, perhaps, ought to have pleased me; but I confess I felt something of the uneasiness of the tailor who said that, whenever a customer’s circumference was either much less, or much more, than at the last measurement, he at once sent in his bill; and I was not consoled until I recollected that, thirteen years ago, in discussing Hume’s essay on “Miracles,” I had quoted, with entire assent, the following passage from his writings:  “Whatever is intelligible and can be distinctly conceived implies no contradiction, and can never be proved false by any demonstrative argument or abstract reasoning a priori."[47]

Now, it is certain that the existence of demons can be distinctly conceived.  In fact, from the earliest times of which we have any record to the present day, the great majority of mankind have had extremely distinct conceptions of them, and their practical life has been more or less shaped by those conceptions.  Further, the notion of the existence of such beings “implies no contradiction.”  No doubt, in our experience, intelligence and volition are always found in connection with a certain material organisation, and never disconnected with it; while, by the hypothesis, demons have no such material substratum.  But then, as everybody knows, the exact relation between mental and physical phenomena, even in ourselves, is the subject of endless dispute.  We may all have our opinions as to whether mental phenomena have a substratum distinct from that which is assumed to underlie material phenomena, or not; though if any one thinks he has demonstrative evidence of either the existence or the non-existence of a “soul,” all I can say is, his notion of demonstration differs from mine.  But, if it be impossible to demonstrate the non-existence of a “substance” of mental phenomena—­that is, of a soul—­independent of material “substance”; if the idea of such a “soul” is “intelligible and can be distinctly conceived,” then it follows that it is not justifiable to talk of demons as “impossibilities.”  The idea of their existence implies no more “contradiction” than does the idea of the existence of pathogenic microbes in the air.  Indeed, the microbes constitute a tolerably exact physical analogue of the “powers of the air” of ancient belief.

Strictly speaking, I am unaware of any thing that has a right to the title of an “impossibility” except a contradiction in terms.  There are impossibilities logical, but none natural.  A “round square,” a “present past,” “two parallel lines that intersect,” are impossibilities, because the ideas denoted by the predicates, round, present, intersect, are contradictory of the ideas denoted by the subjects, square, past, parallel.  But walking on water, or turning water into wine, or procreation without male intervention, or raising the dead, are plainly not “impossibilities” in this sense.