=The Comparative Lengths of the Three General Periods:= Ancient Philosophy, 625 B. C.–476 A. D. Mediæval Philosophy, 476 A. D.–1453 A. D. Modern Philosophy, 1453 A. D.–the present time. These are the three general periods into which the history of philosophy naturally falls. The two dates that form the dividing lines between these three periods are 476, the fall of old Rome, and 1453, the fall of new Rome (Constantinople). From this it will be seen that 1000 years of mediæval life lie between antiquity on the one side and 450 years of modern times on the other. Whatever value may be put upon the respective intellectual products of these three periods, it is important to note the great difference in their time-lengths. It is 2500 years since philosophical reflection began in Europe. Only 450 of these years belong to modern times. In other words, after the European man grew to reflective manhood, two fifths of his life belong to what is known as ancient civilization, two fifths to mediæval, and only one fifth to modern civilization. =The Real Differences of the Three General Periods.= The differences between these three periods of the reflective life of the European have been very real. They are not to be explained by merely political shiftings or economic changes; nor are they fully expressed as differences in literary or artistic productions. Their differences lie deeper, for they are _differences of mental attitude_. The history of philosophy is more profound, more difficult, and more human than any other history, because it is the record of human points of view. A good deal of sympathetic appreciation is demanded if the student takes on the attitude of mind of ancient and mediæval times. One cannot expect to be possessed of such appreciation until one has traversed the history of thought through its entire length.