After an introduction which covered the nature and branches of philosophy—discussing how philosophy became wrongly divorced from science in modern thought—we talked about the nature of Logic, its division into natural and artificial, the doctrine of Logic and the art of Logic, and the division of the one science of Logic into Formal and Material studies. We said that things in reality have certain properties which characterize them, but as they exist in the intellect they take on new properties which can be utilized to bring out new knowledge. We saw that a perfect process of reasoning validly concludes to new knowledge but also that such a conclusion can be of varying grades of certitude. We talked about how Formal Logic is interested in those logical properties which are necessary to correctly bring out conclusions from our old knowledge, while Material Logic is interested in those logical properties (e.g., genus, species, property, definition, division, demonstration, probability, etc.) which are responsible for different degrees of certitude in our valid reasoning. We saw that while Logic and its arguments appeal only to the intellect by means of intellectual evidence—some arguments leading to absolutely certain knowledge in demonstration, some leading to various degrees of probability in dialectics—there are also attempts in human discourse to force one to accept a conclusion by appealing, not only to the intellect, but to the will and the emotions: this is the domain of Rhetoric and Politics which depend upon the study of Psychology because they are concerned with the interaction between intellect, will, and sensitive appetites.
We’ve made a distinction between the operations of the intellect, the products of those operations, and the signs of those products. Beginning with simple apprehension, we’ve examined the nature of this operation and its product, the concept. We saw the first two logical properties that every nature acquired when it is conceived by the mind: comprehensive content and extension. Following our general procedure of definition then division, now that we’ve covered the concept in general, we will divide the concept into its various kinds according to its various logical relationships.