There is no escape from the law of identity, neither in the universe with which
[one] deals nor in the working of his own consciousness, and if he is to
acquire knowledge of the first, he must discover the proper method of using the
second; . . . there is no room for the arbitrary in any activity of man,
least of all in his method of cognition—and just as he has learned to be
guided by objective criteria in making his physical tools, so he must be guided
by objective criteria in forming his tools of cognition: his concepts.