Evidently common sense had nothing to fear from religious faith of this character; but the matter could not end there.  Common sense is not more convinced of anything than of the difference between good and evil, advantage and disaster; and it cannot dispense with a moral interpretation of the universe.  Socrates, who spoke initially for common sense, even thought the moral interpretation of existence the whole of philosophy.  He would not have seen anything comic in the satire of Moliere making his chorus of young doctors chant in unison that opium causes sleep because it has a dormitive virtue.  The virtues or moral uses of things, according to Socrates, were the reason why the things had been created and were what they were; the admirable virtues of opium defined its perfection, and the perfection of a thing was the full manifestation of its deepest nature.  Doubtless this moral interpretation of the universe had been overdone, and it had been a capital error in Socrates to make that interpretation exclusive and to substitute it for natural philosophy.  Locke, who was himself a medical man, knew what a black cloak for ignorance and villainy Scholastic verbiage might be in that profession.  He also knew, being an enthusiast for experimental science, that in order to control the movement of matter—­which is to realise those virtues and perfections—­it is better to trace the movement of matter materialistically; for it is in the act of manifesting its own powers, and not, as Socrates and the Scholastics fancied, by obeying a foreign magic, that matter sometimes assumes or restores the forms so precious in the healer’s or the moralist’s eyes.  At the same time, the manner in which the moral world rests upon the natural, though divined, perhaps, by a few philosophers, has not been generally understood; and Locke, whose broad humanity could not exclude the moral interpretation of nature, was driven in the end to the view of Socrates.  He seriously invoked the Scholastic maxim that nothing can produce that which it does not contain.  For this reason the unconscious, after all, could never have given rise to consciousness.  Observation and experiment could not be allowed to decide this point:  the moral interpretation of things, because more deeply rooted in human experience, must envelop the physical interpretation, and must have the last word.

It was characteristic of Locke’s simplicity and intensity that he retained these insulated sympathies in various quarters.  A further instance of his many-sidedness was his fidelity to pure intuition, his respect for the infallible revelation of ideal being, such as we have of sensible qualities or of mathematical relations.  In dreams and in hallucinations appearances may deceive us, and the objects we think we see may not exist at all.  Yet in suffering an illusion we must entertain an idea; and the manifest character of these ideas is that of which alone, Locke thinks, we can have certain “knowledge”.