into which it was said some of the disciples of Descartes were brought by this same preliminary assumption of their master—a sufficient _reductio ad absurdum_ of the favourite postulate which leads to it. To act upon it would argue insanity in the agent; it must therefore be empty verbal speculation. So Reid further argued. But even this solitude is not the last issue of Reid’s _bête noire_. The system in which I have been educated, he said, not only leaves me absolutely alone; _it extinguishes me_, along with the external universe of things and persons; it is at last literally suicidal. It transforms persistent personal existence into a mere succession of unconnected sensations and ideas. If the magic circle of sensations and ideas, within a self that persists amidst perpetual changes, cannot be broken through, then even this supposed ‘self’ must be an illusion, and the word self must be meaningless. The personal pronoun ‘I,’ as well as the personal pronoun ‘you,’ are both alike unmeaning. The universe resolves at last, not merely into sensations that are all referable to myself, but into sensations without any self—into isolated sensations—which seem indeed to follow one another in an orderly way, but without any guarantee that the seeming order is more than transitory, or that the illusory cosmos may not at any moment become chaos. Is there nothing within the resources of reason to arrest this intellectual suicide? Has reason got anything to show in justification of this preliminary sacrifice of a conviction on which men have to act, whatever their theories may be? Must I surrender the conviction, that when I am seeing or touching I am actually having revealed to me something that is extended and solid, and that, _as such, must_ be more and other than the private sensations and ideas of the person that is seeing and touching? Must this conviction, and others like it, on which human experience practically depends, be all sacrificed on the altar of authority and conjecture? This had been the question around which Reid’s thoughts were revolving in the twenty years preceding the publication of his book. ‘For my own satisfaction,’ he tells us, ‘I entered into a serious examination of the principles upon which this sceptical system is built; and was not a little surprised to find that it leans with its whole weight upon a hypothesis which is ancient indeed, and hath been very generally received by philosophers, but of which I could find no solid proof. The hypothesis I mean is—that we do not really perceive things that are external, but only certain images and pictures of them imprinted upon the mind, which are called “impressions” and “ideas.” I thought it unreasonable, upon the authority of philosophers, to admit an hypothesis which, in my opinion, overturns all philosophy; all religion and virtue, and all common sense; and I resolved to inquire into this subject anew, without regard to any hypothesis.’