I have tried in this little volume to explain aesthetic preference, particularly as regards visible shapes, by the facts of mental science. But my explanation is addressed to readers in whom I have no right to expect a previous knowledge of psychology, particularly in its more modern developments. I have therefore based my explanation of the problems of aesthetics as much as possible upon mental facts familiar, or at all events easily intelligible, to the lay reader. Now mental facts thus available are by no means the elementary processes with which analytical and, especially experimental, psychology has dealings. They are, on the contrary, the everyday, superficial and often extremely confused views which practical life and its wholly unscientific vocabulary present of those ascertained or hypothetical scientific facts.