From the philosophic side it is sometimes urged that we cannot reason from the phenomenal to the noumenal, from the world of appearance to the world of reality; that consequently nothing happening in the material world can prove the existence of a spiritual one. But this is easily answered. We cheerfully agree, with Kant, that a spiritual world cannot be proved coercively and in such knock-down fashion that belief cannot be avoided. But it can be proved in the same way and to the same extent as many other things which we believe and find ourselves justified in believing. For instance, atoms and electrons and the Ether of Space are not phenomenal; no one has ever seen or heard or felt or smelt them; but we infer their real existence from the behaviour of the matter which does affect our senses. Again: we cannot _prove_ to ourselves that other human beings exist, or even that an external world exists; my experience may be a huge subjective hallucination. If I were reading this paper I should not be able to prove to myself that any other mind was present. Looking around, I should receive certain impressions--sensations of sight--and I should call certain aggregations of these the physical bodies of beings like myself. From the similarity of their structure and behaviour to the structure and behaviour of my own body, I should infer that they have got minds somehow associated with them, as my mind is associated with my body. But you could not prove it to me. If you got angry with my obstinacy, and knocked me down, I should experience painful sensations, but the existence of a mind external to me--and an angry one--would still be a matter of inference only. But we find that the inference is justified. We find that it "works," and social life is possible. For the purposes, then, both of science and of ordinary life, we do reason from phenomenon to noumenon, from appearance to reality, from attribute to substance; and our reasoning justifies itself. I affirm, therefore, that the kind of proof which we as psychical researchers put forward for the existence of and communication from discarnate minds, is philosophically the same kind as the proof we have of the existence of incarnate minds. If a short and clear exposition of the point is required, free from any psychical-research bias, I may refer inquirers to the chapter on the Psychological Theory of an External World in J. S. Mill's _Examination of Sir William Hamilton's Philosophy_. Our evidence may be insufficient to justify belief--in the opinion of many, it is--and I blame no one for disbelieving; but it is evidence. And if it sufficiently accumulates and improves in quality, it may amount to a degree of proof at least comparable with that concerning electrons, which are now accepted as real by all physicists. One or two difficulties may here be briefly referred to: