Here is not the place to show the palpable advantages of the methods of abstract thought and especially of the abstract thought-operations with pure forms. It is sufficient to characterise its main principle of procedure. We may also parenthetically remark that from our position we are no longer in need of axioms either in mathematics or in any other formal science. The data of formal sciences are certain mental operations, viz. positing pure forms, and combining, separating, and recombining them. The subject matter of formal sciences consists in the products of these operations. To formulate some of the simplest products in axioms is a mistake which has been pointed out by Hermann Grassmann in his _Ausdehnungslehre_. We are struck and overawed with the cosmic order of all natural phenomena which, as science teaches, is produced through the rigidity of the formal laws of existence. The planetary system with its regularity of motion which in spite of its many complications has been formulated by Kepler in most simple laws is an object of wonder to us. This order of nature is the same order as the grand harmony that prevails in mathematics and all the other formal sciences. The most complicated laws of both, forms of nature and forms of thought, are nothing but generalisations of special applications of the principle of identity in some kind of action that takes place. While the order of the objective world excites our wonder we can understand the order of the subjective world of thought-forms and know that, being the product of certain mental operations according to the principle of identity, it must be a matter of course. Thus the intrinsic necessity of the laws of our thought-forms gives us a clue to the intrinsic necessity of the laws of nature. III. CONSERVATION OF MATTER AND ENERGY, AND CAUSATION.