planets, and we therefore say that "it is a planet." Similarly we may say that "the planets are bodies revolving in elliptic orbits," but only a part of the whole number so revolving. Nevertheless it follows that if the earth is among the planets, and the planets among bodies revolving in elliptic orbits, that the earth is among the latter. A very elementary knowledge of chemistry enables us to argue similarly concerning the following;— Iron, Elementary substances. Iron is one of the metals, and metals are elements or simple undecomposable substances, in the sense of being among them or a part of them, but not as composing the whole. It follows necessarily that "Iron is one of the elementary substances." We have had then two examples of a fixed and necessary form of thought which is necessary and true whatever the things may be to which it is applied. The form of argument may be expressed in several different ways, and we shall have to consider it minutely in the lessons on the syllogism; we may express it, for instance, by saying that "part of a part is part of the whole." Iron is part of the class of metals, which is part of the class of elements: hence iron is part of the class of elements. If I now introduce another definition of Logic and say that it is "the science of the necessary forms of thought," the reader will I hope clearly apprehend the meaning of the expression "necessary forms of thought." A form is something which may remain uniform and unaltered, while the matter thrown into that form may be varied. Medals struck from the same dies have exactly the same form, but they may be of various matter, as bronze, copper, gold or silver. A building of exactly the same form might be constructed either of stone or bricks; furniture of exactly similar shape may be made of oak, mahogany, walnut wood, etc. Just as we thus familiarly recognize the difference of form and substance in common tangible things, so we may observe in Logic, that the form of an argument is one thing, quite distinct from the various subjects or matter which may be treated in that form. We may almost exhibit to the eye the form of reasoning to which belong our two latter arguments, as follows: (Y) (X)......is......(Z) If within the three pairs of brackets, marked respectively X, Y and Z we place three names, such that the one in place of X may be said to come under that in Y, and that in Y under that in Z, then it necessarily follows that the first (X) comes under the last (Z). Logic, then, is the science occupied in ascertaining and describing all the general forms of thought which we must employ so long as we reason validly. These forms are very numerous, although the principles on which they are constructed are few and simple. It will hence appear that logic is the most general of all the sciences. Its aid must be more often required than the aid of any other science, because all the particular sciences treat portions only of existing things, and create very different and often unconnected branches of knowledge. But logic treats of those principles and forms of thought which must be employed in every branch of knowledge. It treats of the very origin and foundations of knowledge itself; and though it is true that the logical method employed in one science may differ somewhat from that em ployed in another science, yet whatever the particular form may be, it must be logical, and must conform to the laws of thought. There is in short something in which all sciences must be similar; to which they must conform so long as they maintain what is true and selfconsistent; and the work of logic is to explain this common basis of all science. ance. One name which has been given to Logic, namely the Science of Sciences, very aptly describes the all extensive power of logical principles. The cultivators of special branches of knowledge appear to have been fully aware of the allegiance they owe to the highest of the sciences, for they have usually given names implying this allegiThe very name of logic occurs as part of nearly all the names recently adopted for the sciences, which are often vulgarly called the "ologies," but are really the "logics," the "o" being only a connecting vowel or part of the previous word. Thus geology is logic applied to explain the formation of the earth's crust; biology is logic applied to the phenomena of life; psychology is logic applied to the nature of the mind; and the same is the case with physiology, entomology, zoology, teratology, morphology, anthropology, theology, ecclesiology, thalattology, and the rest*. Each science is thus distinctly confessed to be a special logic. The name of logic itself is derived from the common Greek word óyos, which usually means word, or the sign and outward manifestation of any inward thought. But the same word was also used to denote the inward thought or reasoning of which words are the expression, and it is thus probably that later Greek writers on reasoning were led to call their science * Except Philology, which is differently formed, and means the love or study of words; the name of this science, if formed upon the same plan, would be logology. ἐπιστήμη λογική, or logical science ; also τέχνη λογική, οι logical art. The adjective λoyikń, being used alone, soon came to be the name of the science, just as Mathematic, Rhetoric, and other names ending in "ic" were originally adjectives but have been converted into substantives. Much discussion of a somewhat trifling character has arisen upon the question whether Logic should be considered a science only, an art only, or both at the same time. Sir W. Hamilton has even taken the trouble to classify almost all the writers on logic according as they held one opinion or the other. But it seems substantially correct and sufficient to say, that logic is a science (in so far as it merely investigates the necessary principles and forms of thought, and thus teaches us to understand in what correct thinking consists; but that it becomes an art when it is occupied in framing rules to assist persons in detecting false reasoning. A science teaches us to know and an art to do, and all the more perfect sciences lead to the creation of corresponding useful arts. Astronomy is the foundation of the art of navigation on the ocean, as well as of the arrangement of the calendar and chronology. Physiology is the basis of the art of medicine, and chemistry is the basis of many useful arts. Logic has similarly been considered as the basis of an art of correct reasoning or investigation which should teach the true method to be observed in all sciences. The celebrated British logician Duns Scotus, who lived in the 13th century, and called logic the Science of Sciences, called it also the Art of Arts, expressing fully its preeminence. Others have thus defined it-"Logic is the art of directing the reason aright in acquiring the knowledge of things, for the instruction both of ourselves and others." Dr Isaac Watts, adopting this view of logic, called his well-known work "the Art of Thinking." It may be fairly said however that Logic has more the form of a science than an art for this reason—all persons necessarily acquire the faculty and habit of reasoning long before they even know the name of logic. This they do by the natural exertion of the powers of mind, or by constant but unconscious imitation of others. They thus observe correctly but unconsciously the principles of the science in all very simple cases; but the contradictory opinions and absurd fallacies which are put forth by uneducated persons shew that this unaided exercise of mind is not to be trusted when the subject of discussion presents any difficulty or complexity. The study of logic then cannot be useless. It not only explains the principles on which every one has often reasoned correctly before, but points out the dangers which exist of erroneous argument. The reasoner thus becomes consciously a correct reasoner and learns consciously to avoid the snares of fallacy. To say that men can reason well without logical science is about as true as to say that they can live healthily without medicine. So they can-as long as they are healthy; and so can reasoners do without the science of reasoning-as long as they do reason correctly; but how many are there that can do so? As well might a man claim to be immortal in his body as infallible in his mind. And if it be requisite to say a few words in defence of Logic as an art, because circumstances in the past history of the science have given rise to misapprehension, can it be necessary to say anything in its praise as a science? Whatever there is that is great in science or in art or in literature, it is the work of intellect. In bodily form man is kindred with the brutes, and in his perishable part he is but matter. It is the possession of conscious intellect, the power of reasoning by general notions that raises him above all else upon the earth; and who |