With Imprimatur. Introduction 1. Definition of Logic. -- Logic is the systematic study of the order to be observed in judging, reasoning, and other processes of thought in order to arrive at the knowledge of truth. This definition shows us: (1) the materials (material cause) of the logical order; (2) their elaboration (formal cause) (3) the purpose of this elaboration (final cause). 2. Materials of Logical Order. -- In some sense, these materials are acts of the mind, like apprehension, judgment, ratiocination (reasoning); but strictly speaking, only apprehensions are the material object of logical order (3). (1) By apprehension the mind represents to itself one thing or many things, without either affirming or denying anything. Concepts; the product of apprehension, are expressed by names or terms. (2) To establish a relation of identity or non-identity, of agreement or non-agreement, between the objects of two concepts, in affirming or denying one object of another is to judge. A judgment is expressed in a proposition. (3) To reason is to combine two or more judgments so as to form a new one. The complete ordinary expression of this simplest exercise of reasoning is the syllogism. 3. The Formal Cause of the Logical Order. -- The formal object of logic, or the point of view from which logic regards the acts of the mind, is their adaptability to certain processes of thought which are called either particular sciences or philosophy. These processes imply stages. The mind must grasp the numerous aspects of reality one after another before coordinating the fragmentary explications. Judgment is the first step in combining ideas; judgments in their turn become the materials of reasoning; an isolated piece of reasoning does not suffice to produce adequate knowledge of things, but several reasonings become materials of a scientific system. This rational arrangement of ideas constitutes the logical order properly so called: "the order which reason constitutes for its own acts". 4. Difference between Psychology and Logic. -- Many different sciences may be concerned with one and the same subject, if they study different properties in it, and, consequently, consider it from different points of view. They are then said to have a common (that is, undetermined) object, but each has its own formal (or determined) object. Psychology, too, has in part for its (material) object the act of human reason, but it does not study them under the same aspect (formal object) as logic does. Psychology sees in them vital acts, of which it seeks the nature and origin. Logic considers them in so far as they are cognitions of objects, objective representations, abstract and universal, furnishing the matter of the relations which reason formulates in judgments and reasonings, and arranges in a scientific system. In psychology, as in all the sciences of the real, order is the necessary condition of science; but logic has this order for its object. Its proper object is the form itself of this scientific construction.