The Principle of Identity is the unchanged text of a lecture given on the occasion of the 500th anniversary of the University of Freiburg im Brisgau, fo the faculty day on June 27, 1957. The Onto-theo-logical Constitution of Metaphysics is the explication that conclude a seminar during the winter semester 1956-57 on Hegel’s Science of Logic. It has in part resived. The lecture took place on February 24, 1957 in Todnauberg. The Principle of Identity glace ahead and backward, too; ahead into the realm from which stems the subject matter of the lecture The Thing (see notes); back to the realm where the essence of metaphysics has its source; the constitution of metaphysics is defined by difference. The close relations of identitty and difference will be shown in this publication to be that which gives us thought. The close relation of idendtity and difference wiill be shown in this publication to be that which gives us thought. The reader is to discover for himself in what way difference stem from the essence of identity, by listening to the harmony presiding over the event of approriation and perdurance. In this realm one cannot prove anything, but one can point out a great deal, Todtnauberg September 9, 1957