Logic
2 of the 7 encyclopedias on this shelf carry an entry for Logic. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
loj'ik, the art of reasoning. Logic enables the student to distinguish between true and false argument. There are many forms of reasoning. One of the simplest is the following: 1. Adams County is a part of Ohio. 2. West Union is a part of Adams County. 3. West Union is a part of Ohio. Such a form is called a syllogism. The first statement is called the major premise; the second, the minor premise; the third, the conclusion. If the premises be true, the conclusion must be true. This sort of reasoning is employed largely in geometry, as: 1. The opposite sides of a parallelogram are equal. 2. This figure is a parallelogram. 3. Its opposite sides are equal. In argument of this sort, liability to error lies chiefly in assuming a false major premise. In the days preceding the American Revolution the British authorities argued as follows: 1. All subjects should pay taxes. 2. The American colonists are subjects. 3. They should pay taxes. The American colonists argued as follows: 1. Only represented subjects should pay taxes. 2. We are not represented. 3. We should not pay taxes. So far as the form of argument is concerned, both syllogisms are correct. The different conclusions drawn are due to starting from contradictory major premises. The early colonists of Virginia sent back their vessels to England loaded down with iron pyrites, or fool's gold. Thrown into a syllogism, their argument was as follows: 1. Gold is yellow. 2. This metal is yellow. 3. This metal is gold. In their syllogisms, both premises are true, but the conclusion does not follow from the premises. It is not true. The metal was not gold. In his unique poem of The Deacon's Masterpiece, or The Wonderful One-Hoss Shay, Dr. Holmes presents two syllogisms, the deacon's and his own. Both are fallacies. The reader may decide whether the fallacies lie in the premises or in the conclusions. The deacon's syllogism is as follows: 1. A shay wears out in its weakest spot. 2. My shay shall have no weakest spot. 3. My shay will not wear out. Holmes's syllogism is the following: 1. All chaises wear out. 2. This chaise had no weak spot. 3. All parts wore out at once. As may be remembered, he leaves the argument with "Logic is logic. That's all I say." In syllogistic argument, we proceed from general statements to a definite one. From "All men are mortal," and "Enoch is a man," the syllogistic logician argues that "Enoch must die." This form of argument is called deduction. Turned end for end , the argument runs, "Enoch died, Columbus died, George Washington died, a million other men have died, hence all men die." In other words, man is mortal. This is called inductive reasoning. The latter is the form employed usually by scientists. When a wheat buyer sends a man to draw a few ounces of wheat from different parts of a car and puts them together as a sample, he infers by inductive reasoning the kind and quality of wheat contained in the car. The more samples he has from the car, the more certain his conclusion. The directors of the United States census have observed that, for the past hundred years or more, the center of population has moved steadily westward from a point near the Atlantic coast to a point in 1900, near the city of Columbus, Indiana. We are justified by induction in concluding that the census of 1910 will locate the center still nearer Indianapolis. This sort of reasoning is open to error. Although we may have seen half the beans in a bag, we cannot be certain that all the beans are sound until we have examined the last one. The more instances we observe, the more certain our conclusion. The early settlers of Minnesota had so many failures and disappointments that they jumped at the conclusion that corn and apples could not be raised in the state. Persistent efforts and a later trial of varieties better adapted to the climate have demonstrated that the logic of the pioneers was utterly at fault. Far from being restricted to the college and the school, it may be said, as of no other subject, that logic, whether deductive or inductive, is but the application of shrewd common sense. Many of our popular sayings are logical conclusions of the shrewdest sort: Where there is so much smoke, there must be some fire. Experience keeps a dear school; fools learn in no other. Light heel'd mothers make leaden heel'd daughters. He that by the plow would thrive, Himself must either hold or drive.
Collier's New Encyclopedia (1921)
as known in the present day, is a development and modification of the art of reasoning, techné dialektikē which Aristotle, utilizing the labors of his predecessors, and notably those of Zeno of Elea, molded into something like consistent shape. The first development of Aristotelian logic was by the Scholastics. At the time of the Reformation, probably as a protest, Scholasticism was depreciated, and at some of the Scotch universities it was discarded for Ramism. The subtle distinctions and keen disputations of the Schoolmen led in the next century to Bacon's condemnation of the perversion-not of the cultivation-of logical pursuits. Locke was not so moderate, as may be seen in his "Essay." continues in gener tre in the antes, 35 ength, 620 e a littlo the sea, e destructi ah the lowe cted by la th. The p Nièvre an ed by th and the the Allier the left. considerab is conned e, and Its valle drainage rtment part COUT capis about ron and riches ies, 12, e cott Bs, papa actured es are by th cound, med The trene eleval rises fiz Generally speaking, down to the first half of the 19th century there was little dispute as to how logic should be defined. The Port Royalists had certainly called it the Art of Thinking ; but the Art or Science of Reasoning, or the Art and Science of Reasoning met with little opposition definition . This is how as a Whately defines it, and a writer of such opposite opinions as Tongiorgi, S. J., as substantially the same words; and a parallel passage to Whately's explanation as to how logic is at once a science and an art, occurs in Liberatore, who is read in many of the ecclesiastical colleges in Rome. Deductive logic, syllogistic logic; in which no more is inferred in the conclusion than is implicitly contained in the premises. Equational logic, a system of logical notation in which propositions are expressed in the form of equations. Inductive logic, the science which treats of inductive reasoning, by which, broadly speaking, a general proposition is inferred from a number of particular propositions. Modified logic, that logic which is concerned in the investigation of truth and its contradictory opposite error; of the causes of error, and the impediments to truth and their removal, and of the subsidiaries by which human thought may be strengthened and guided in its functions.