Ideas resemble coins which have a certain exchange value according to written and unwritten laws. Some are copper coins, so defaced and dirty that no one would suspect from their looks that they had once sparkled like bright gold. Others shine even to-day, after a lapse of a thousand years, and a commanding figure proudly proclaims its origin. One might even more aptly say that ideas resemble securities that are highly valued to-day and may be worthless to-morrow; one day they promise their possessor wealth and fame, and the next day there comes a spiritual break, he is impoverished, and is left with an apparently worthless piece of paper.... There is as yet, alas! no standard by which the values of different ideas might be measured. Every man constructs for himself without much ado a canon whereby to value his own thoughts. As a rule he swims with the tide of current opinion; more rarely he goes with the minority and very rarely he independently makes his own measure wherewith to judge matters. Strange! In the end the conflict of minds turns altogether about ideas and their estimation. What else do geniuses, the pathfinders of mankind, accomplish but to disseminate a hitherto neglected or even unknown idea and cause it to be generally accepted or to cause ideas that have hitherto stood high in the world’s estimation to topple from their thrones? Just as everything else in life runs a circuitous course, in which beginning and end touch, so is it also with the valuation of ideas. Not only the genius, but the fool also strips old, highly esteemed ideas and overvalues others that he has created for himself. The genius and the fool agree in that they permit themselves to be led by the “overvaluation” of their ideas. This expression was coined in a happy moment by the psychiatrist Wernicke. It tells more in its pregnant brevity than a long-winded definition would. Formerly it was the custom to speak of the “fixed ideas” of the sufferers from the peculiar form of insanity which physicians call “paranoia,” the mental disease which the laiety knows better and understands less than any other psychosis. A delusion was regarded as a fixed idea which neither experience nor logic could shake. To-day we have penetrated deeper into the problems of delusions. We know that ideas differ from one another tremendously. Some are anemic and colourless, come like pale shadows and so depart. Others have flesh and blood and scintillate in brilliant colours. Long after they have vanished, their image still trembles in our souls in gently dying oscillations. The explanation for this phenomenon is very simple. Our attention is dependent upon our emotions. Pale thoughts are indifferent and have no emphasis. Coloured ideas are richly endowed with emotions, being either pleasurable or painful.