To one not philosophically inclined, idealism seems a rather fantastic doctrine—one quite obviously false. The great Dr. Johnson thought he could adequately refute it by kicking his toe against a stone. In one form or another, however, it has existed wherever men have thought deeply on the fundamental nature of mind and of the external world. One cannot go far in a study of the sources of knowledge without becoming aware that the only immediate evidence of external objects lies in our sense impressions. The mind has no way of putting itself in contact with things external to itself except through the five senses. Up to this point there is fairly general unanimity. The difficulty lies in correctly interpreting this fact.