ABSTRACT
A true classification includes in each class, those objects which have more characteristics in common with one another, than any of them have in common with any objects excluded from the class. The broadest natural division among the Sciences, is the division between those which deal with the abstract relations under which phenomena are presented to people, and those which deal with the phenomena themselves. Relations of whatever orders, are nearer akin to one another than they are to any objects. Objects of whatever orders, are nearer akin to one another than they are to any relations. The truths reached through the first kind of inquiry, though concrete inasmuch as they have actual existences for their subject-matters, are abstract inasmuch as they refer to the modes of existence apart from one another; while the truths reached by the second kind of inquiry are properly concrete, inasmuch as they formulate the facts in their combined order, as they occur in Nature.
