a tablet, whether born blank or with characters stamped on it, has even an apparent meaning. A metaphor, interpreted as a fact, becomes the basis of his philosophical system. [1] Cf. Locke’s own statement (Book III. c. iv. sec. 10). ‘The cause of any sensation, and the sensation itself, in all the simple ideas of one sense, are two ideas; and two ideas so different and distant one from another, that no two can be more so.’ Does the mind make impressions on itself? 15. As applied to the ideas of reflection, indeed, the metaphor loses even its plausibility. In its application to the ideas of sensation it gains popular acceptance from the ready confusion of thought and matter in the imaginary cerebral tablet, and the supposition of actual impact upon this by ‘outward things.’ But in the case of ideas of reflection, it is the mind that at once gives and takes the impression. It must be supposed, that is, to make impressions on itself. There is the further difficulty that as perception is necessary in order to give an _idea_ of sensation, the impress of perception must be taken by the mind in its earliest receptivity; or, in other words, it must impress itself while still a blank, still void of any ‘furniture’ wherewith to make the impression. There is no escape from this result unless we suppose perception to precede the idea of it by some interval of time, which lands us, as we have seen, in the counter difficulty of supposing an unperceived perception. Locke disguises the difficulty from himself and his reader by constantly shifting both the receptive subject and the impressive matter. We find the ‘tablet’ perpetually receding. First it is the ‘outward part’ or bodily organ. Then it is the brain, to which the impression received by the outward part must somehow be continued, in order to produce sensation. Then it is the perceptive mind, which takes an impression of the sensation or has an idea of it. Finally, it is the reflective mind, upon which in turn the perceptive mind makes impressions. But the hasty reader, when he is told that the mind is passively impressed with ideas of reflection, is apt to forget that the matter which thus impresses it is, according to Locke’s showing, simply its perceptive, _i.e._ its passive, self. Source of these difficulties. The ‘simple’ idea, as Locke describes it, is a complex idea of substance and relation.