The Sophists had proposed rules of practical value in the study of individual cases; Socrates had tried to fix upon some universal principle as the basis of knowledge; Aristotle made a comprehensive study of the regular forms of thought and the rules that govern the arrangement of these forms in right thinking. In true Platonic fashion he conceived physical events in nature to be due to some universal cause. If, therefore, logical procedure be scientific, it must follow the ways of nature: logic must deduce particular perceptions from some universal idea. The necessary thought-relations in which the particular stands will then appear. Deduction of the particular from the universal is the true scientific method, used in the explanation of nature-phenomena; so in proof the same deductive reasoning should be used. In scientific study we are trying to show the conceptual necessity of an empirical fact; in proof we are showing the conceptual necessity of the particular term. Whether we are explaining an event or proving a conclusion, we are employing the same logical process. Aristotle thus regarded his logic as the true scientific method for practical service, not as a merely abstract discipline in verbal hair-splitting. Socrates and Plato confined themselves to the study of the concept or simple term. Aristotle also studied the concept. Indeed, he tried to find out what concepts are fundamental in our thinking, so fundamental that they are our thought reduced to its lowest terms. He names ten of these fundamental concepts and calls them categories. But Aristotle goes farther than Socrates and Plato, and makes his real point of departure the judgment. A single term does not express truth. For truth we must have two terms connected by the verb “is,” _i. e._ some _relation_ must be shown between them. This is a judgment. Reasoning is still more complex. It is the putting together or showing the relation between two judgments. This process takes the form of the syllogism. The first task of deduction is to present the laws of the syllogism. These will then be the laws of scientific investigation. According to these, particulars can be derived with certainty from universal propositions, provided such universals are established. The syllogism is in the form of two premises and a derived conclusion. It contains three terms. The problem is to infer, from the relation that one of these terms bears to the two other terms, what the two bear to each other. The principle employed is that of subordination; and the differentiations of the syllogism can be many, depending on the quality and quantity of the premises and the distribution of the middle term. The working of the syllogism in inference has a certainty so great that Aristotle called it apodictic.