REASONING is a special kind of mental process, different from other mental processes such as remembering, imagining, hoping, or fearing. All mental processes are studied by psychologists, but reasoning is the only one of interest to logicians. Psychologists and logicians are both concerned with the reasoning process, but from quite different points of view. To explain the difference in their approaches to it, we must first analyze the reasoning process itself.
Reasoning is the kind of thinking performed in solving problems. It is a special kind of thinking in which one proposition is arrived at and affirmed to follow from one or more other propositions accepted as the starting point of the process. The proposition thus arrived at is called the "conclusion," and the propositions from which it is claimed to follow are called "premisses." Reasoning can be characterized as the process of drawing conclusions from premisses.
As psychologists study the reasoning process they find it to be extremely complex. It involves memory and motivation as well as intelligence, and is intimately connected with the emotional life of the reasoner. Reasoning is but one activity of man, and is related to his other activities in many ways. These aspects of the reasoning process are all of importance to psychology.
The logician, on the other hand, is not concerned with any relationships between the activity of reasoning and the other activities and interests of man-except possibly to the end of distinguishing them clearly. Logic does not deal with the process of reasoning, but only with methods for appraising the correctness of the completed process. Reasoning may be either correct or incorrect: it is correct if the premisses provide good evidence for the truth of the conclusion inferred from them, otherwise it is incorrect. This distinction between correctness and incorrectness is the central problem of reasoning with which logic deals. The logician's methods and techniques have been developed to accom