All other so-called standards are derived from the abstract ideas of literary genres and of rhetorical categories. It is easy to judge of a new tragedy if you know what a tragedy ought to be, if you have a catalogue of purely external characteristics which you may either find, or not find, in the new work that comes before you. This is, of course, the crudest form of rhetorical criticism; there is another which is not less frequent, but more subtle. The critic builds up an ideal of what art ought to be, not with abstract categories, and classifications transformed into arbitrary æsthetic precepts or standards, but through his predilection for one particular author, or for one particular epoch, the Middle Ages or the Renaissance, the Classics or the Romantics: every work of art which is different either in spirit or in form from those that have been chosen is condemned in proportion to its variation from the ideal. This form of criticism is often also vitiated by the intrusion of intellectualistic and moralistic errors, since an ideal which is a mere particular determination of the past assumed as a universal value is likely to be mere rhetoric of thought and morality as well as of art. The only legitimate standard in æsthetic criticism is the æsthetic standard, that of beauty or expression, as against ugliness or non-expression. Our critical judgment is the reaction of our æsthetic personality in the presence of a work of art, as the moral judgment is the reaction of our moral personality in the presence of an action. Our knowledge of a work of art, of a concrete and individual intuition, as our knowledge of an action, approaches more or less to the ideal limit, according to the breadth of our experience and the depth of our understanding; but there exist no external criteria on which we can rest our judgment, no mechanical props which will support it. This theory of criticism, far from justifying a capricious and arbitrary subjectivism, requires from the critic a constant vigilance against that which is narrowly personal, capricious, and arbitrary in himself; a patient, unceasing effort in the labor of recapturing and recreating the material and spiritual circumstances from which the work of art originally sprang; and the quick sensitivity of the artist coupled with the wide understanding of the historian and the philosopher.