But such fancies are not limited to the minds of the ingenuous and inattentive; they constitute the base of that error owing to which a distinction of periods, which shall be what is called _objective and natural_, is desired and sought after. Christian chronographers had already introduced this ontological meaning into chronology, making the millenniums of the world's history correspond with the days of the creation or the ages of man's life. Finally, Ferrari in Italy and Lorenz in Germany (the latter ignorant of his Italian predecessor) conceived a theory of historical periods according to generations, calculated in periods of thirty-one years and a fraction, or of thirty-three years and a fraction, and grouped as tetrads or triads, in periods of a hundred and twenty-five years or a century. But, without dwelling upon numerical and chronographic schemes, all doctrines that represent the history of nations as proceeding according to the stages of development of the individual, of his psychological development, of the categories of the spirit, or of anything else, are due to the same error, which is that of rendering periodization external and natural. All are mythological, if taken in the naturalistic sense, save when these designations are employed empirically--that is to say, when chronology is used in chroniclism and erudition in a legitimate manner. We must also repeat a warning as to the care to be employed in recognizing important problems, which sometimes have first appeared through the medium of those erroneous inquiries, and as to the truths that have been seen or caught a glimpse of by these means. This exempts us (as we remarked above in relation to the criteria of choice) from examining those doctrines in the particularity of their various determinations, because in this respect, if their assumption be obviously fantastic, their value is consequently _nil_. _Nil_, as the value of all those æsthetic constructions is _nil_ which claim to pass from the abstractions, by means of which they reduce the organism of the work of art to fragments for practical ends, to the explanation of the nature of art and to the judgment and history of the creations of human imagination.