"As to _your own_ Ideas," he continued, "know that their relation to yourself is, in their eyes, widely different from what you conceive it to be. Between yourself and them there is the utmost divergence of view on this matter. Under no circumstances whatsoever will they consent to regard themselves as your _property_, and no claim of that kind, nor even the semblance of a claim, must ever be suffered to appear in your dealings with these ghosts. Remember that your common-sense is their metaphysic, and their metaphysic your common-sense; what you dream of, they see; what you see, they dream of; and the consequence is that many truths, which appear to you as the least certain of your conclusions, are used by them as the familiar axioms of thought. On the other hand, what are axioms to you are often problems to them. Your _cogito ergo sum_, for example, will not go down in the spiritual world. For just as you, on your side of the theory of knowledge, are busy in trying to account for your Ideas, so they, on theirs, have much ado in their efforts to account for _you_; all of them find you the most illusive of beings, while some, as I have already hinted, deny your existence altogether, or treat you as a highly questionable hypothesis. With several of your leading Ideas I hope to make you personally acquainted this very night. To convince them of your identity will be no easy matter, and the most vigilant circumspection will be necessary on your part. I counsel an attitude of uttermost modesty; anything else is certain to give them the impression that you are an impostor. Betray, then, not the least surprise on finding yourself treated by your own Ideas as a being of little importance to their concerns. Above all, you must not expect them to take more than a passing interest in _your brain_. Your best course is to avoid all reference to that topic. 'The brain' is seldom, if ever, mentioned in the best circles of the spiritual world--to which circles, I assume, your leading Ideas belong. You must never forget that in the realm of Ideas class distinctions are rigidly observed; there is an aristocracy and a proletariat, with all the intermediate grades; and many topics which may be safely mentioned among the commons are an offence when introduced to the nobility. 'The brain' is one of these. Its use, among the ghosts, is confined exclusively to the working class; and you will commit a breach of good manners by flaunting its functions in the presence of august society. Were you, for example, in the course of some conversation with a noble Principle, to offer him the use of your own brain, or to suggest that he was in need of such an implement, or in the habit of using it, you would commit an indiscretion of the first magnitude; and it is certain the offended spirit would strike you off his visiting list and decline to haunt you any more. Pardon my insistence on this point. Knowing, as I do, how apt you are to talk about your brain, I am naturally