“So you were pursuing an idea,” said the little man as they emerged into the narrow street.  “Now ideas may be divided variously into classes, as, for instance, ideas which are good, bad, or indifferent.  Or you may contrast the idea of Plato with ideas anything but platonic—­take it as you please.  Then there is my idea, which is in itself, good, interesting, and worthy of the embalming process; and there is your idea, which I am human enough to consider altogether bad, worthless, and frivolous, for the plain and substantial reason that it is not mine.  Perhaps that is the best division of all.  Thine eye is necessarily, fatally, irrevocably evil, because mine is essentially, predestinately, and unchangeably good.  If I secretly adopt your idea, I openly assert that it was never yours at all, but mine from the beginning, by the prerogatives of greater age, wider experience, and immeasurably superior wisdom.  If you have an idea upon any subject, I will utterly annihilate it to my own most profound satisfaction; if you have none concerning any special point, I will force you to accept mine, as mine, or to die the intellectual death.  That is the general theory of the idea.”

“And what does it prove?” inquired the Wanderer.

“If you knew anything,” answered Keyork, with twinkling eyes, “you would know that a theory is not a demonstration, but an explanation.  But, by the hypothesis, since you are not I, you can know nothing certainly.  Now my theory explains many things, and, among others, the adamantine, imperishable, impenetrable nature of the substance vanity upon which the showman, Nature, projects in fast fading colours the unsubstantial images of men.  Why do you drag me through this dismal passage?”

“I passed through it this morning and missed my way.”

“In pursuit of the idea, of course.  That was to be expected.  Prague is constructed on the same principle as the human brain, full of winding ways, dark lanes, and gloomy arches, all of which may lead somewhere, or may not.  Its topography continually misleads its inhabitants as the convolutions of the brain mislead the thoughts that dwell there, sometimes bringing them out at last, after a patient search for daylight, upon a fine broad street where the newest fashions in thought are exposed for sale in brightly illuminated shop windows and showcases; conducting them sometimes to the dark, unsavoury court where the miserable self drags out its unhealthy existence in the single room of its hired earthly lodging.”

“The self which you propose to preserve from corruption,” observed the tall man, who was carefully examining every foot of the walls between which he was passing with his companion, “since you think so poorly of the lodger and the lodging, I wonder that you should be anxious to prolong the sufferings of the one and his lease of the other.”

“It is all I have,” answered Keyork Arabian.  “Did you think of that?”