But before proceeding further, I must remark, in passing, that the difference between the essence of one thing and the essence of another thing is the same as that which exists between the reality or existence of one thing and the reality or existence of another; therefore, if we wished to conceive the existence, for example, of Adam, simply by means of existence in general, it would be the same as if, in order to conceive his existence, we went back to the nature of being, so as to define Adam as a being.