constitution, and the circumstances of the moment, which may greatly modify the action of the former upon the latter. Obviously, this is the business of sheer empiricism, being in many instances no better than guess-work. In Chemistry, we go a step higher, as it is necessary to attend, at most, to the qualities or elements of but one class of objects; still, we never can know that the analysis is complete, or the observation perfect, and are therefore obliged to grope our way by experiment and very limited induction, perhaps never establishing a universal principle by a priori evidence. In the science of Mechanics, we make a great advance, as many abstractions are employed, friction, the rigidity of materials, and the resistance of the air, being generally put aside; mathematical reasoning here comes into play, which had no application in the former sciences, and our conclusions are more abstract, more general, and therefore less practically available. In Celestial Mechanics, it happens curiously, that the abstractions are, as it were, ready-made by nature, gravitation being the sole quality that it is necessary to take into view. Friction and a resisting medium-though of this last there may be some doubt are eliminated by the nature of the case; the problem is complicated only by the gravitating effect of different bodies on each other. Our conclusions are very general, then, but also very limited, as they relate exclusively to position and motion. Astronomy, it was remarked many years ago, is a perfect science; and so it is, the theory of it, though the improvement of instruments is daily bringing to light new facts. Thus it appears, that we approximate the sphere of metaphysical evidence and demonstrative reasoning just in proportion as we leave the world of realities and facts, and abandon the consideration of objects in their entireness, or in all their relations. LECTURE II. THIS DISTINCTION APPLIED TO PHILOSOPHY AND THEOLOGY. In my last Lecture, I endeavoured to define and distinguish the nature and scope of physical and metaphysical inquiry,—to show that the one was properly confined to matters of fact, and the other to relations of ideas. Demonstrative reasoning, I attempted to prove, belongs exclusively to the latter, and its conclusions are always abstract; the truths of physical science are obtained only by the inductive method, by observation and experiment, and by generalizations extending from individuals to a class. Yet the former method has no superiority over the latter, when considered simply as a foundation of belief. Both alike command our assent on indisputable grounds, though the media of proof are radically unlike. Sensible evidence and inductive. reasoning, it is true, admit of degrees, and lead to all shades of belief, from the faintest probability up to what is called moral certainty. Demonstrative reasoning, on the other hand, has no degrees; a proposition is established by it either conclusively or not at all. If successful, it would be contradictory and absurd to deny the conclusion, the proof being then equivalent, but not superior, to that which in the former case renders a fact morally certain. To adopt Locke's distinction between insanity and idiocy, we might say that only a madman can reject a mathematical proof after it has been once explained to him, while to be incapable of governing one's conduct by that sensible evidence which controls the actions of our fellows is simple idiocy. - Such a person is usually said to be incapable of keeping out of fire and water, because he is not able to learn from induction, or repeated experiment, that the former will burn and the latter will drown him. A very brief glance at the history of science was intended to show, that most of the mistakes, retrogressions, and absurdities which have hindered the progress of it may be traced to ignorance or forgetfulness of the distinction here pointed out, to an attempt to deduce facts from abstract conceptions, or to draw down pure ideas to sensible observation and material tests, to calling for demonstration in physics, or following the guidance of the senses only in metaphysical investigations. Illustrations of this error might easily be multiplied from the whole domain of science and speculation, not less numerous and apt in our own day, perhaps, than they were among the ancients or in the times of the schoolmen; but less conspicuous, affecting a smaller class of minds, and therefore less likely, we may hope, to be chronicled for the mingled amusement and pity of future generations. They are now the follies of a sect, a party, or a clique, — usually a small one; while in former days they were the indications of a universal evil, proceeding from illformed habits of thought, and offering a far-extended and almost insuperable barrier to the progress of knowledge. Leaving the task of mere illustration, then, I proceed to inquire how far the distinction now pointed out may be made available for one great purpose of these lectures,—to determine clearly the respective limits of religion and philosophy. It is obvious that the latter term, which is often applied very generally to the pursuit of all knowledge, must here be used in a restricted sense, and be made synonymous, in fact, with metaphysics. It cannot be defined more clearly without a tedious enumeration of all the questions and problems which it comprehends. It is concerned with the origin and explication of our ideas of cause, power, infinity, knowledge, free-will, identity, substance, and the like, all of which are pure abstractions, so that we must reason about them demonstratively, or not at all. Philosophy, in this narrow meaning of the word, includes precisely that class of sub jects which Milton assigned for contemplation to one band of the spirits fallen from heaven, who, in their place of punishment, "apart sat on a hill retired, In thoughts more elevate, and reasoned high All science proceeds from one generalization to another, and must therefore end at a point, in a science that surveys the basis of all the others, determines their proper relations, and binds the whole into one orderly system of knowledge. This seems to have been Lord Bacon's conception of the matter, when, in his general scheme of knowledge, he says, "The basis is Natural History, the stage next the basis is Physics, the stage next the vertical point is Metaphysics." To examine in turn all the questions with which metaphysical philosophy is conversant, so as to exhibit their abstract character, would be a long and, it may be, an unprofitable undertaking. I shall not attempt it, as the fact, perhaps, is apparent enough from a mere enumeration of the subjects, and because all of them which are immediately connected with my principal theme will come up for subsequent consideration. It will be enough for the present briefly to allude to a few of them, the purely ideal character of which may perhaps be questioned. And here a distinction is to be made, as one portion of what is usually called the philosophy of mind is certainly occupied with matters of fact, and comes within the province of inductive reasoning. Psychology is the latest designation in use, and perhaps the most convenient one, for that science which bears the same relation to mind that Anatomy and Physiology do to our corporeal nature. Certainly there are facts of consciousness, no less than those which are evident to sense; the human mind, to a certain extent, is a subject of observation and experiment, as the supposed seat or origin of various phenomena that admit of number, arrangement, and classification. These phenomena, again, are not produced fortuitously, or at random, but are subject to fixed laws, more or less obvious, that may be definitely expressed. I need only refer to the great laws of association, or suggestion, which every one has occasion to observe who seeks to call up subjects that are related to each other, or to discipline his memory. The phenomena of mind, also, are often complex, and need to be analyzed and reduced to their simplest elements. Imagination, for instance, is a compound faculty, embracing simple suggestion, conception, or the picturing forth of an object, abstraction, and the power of forming novel combinations from the elements thus obtained. I speak of this science as confined entirely to mind, without forgetting that one important point in it is the question, whether there be any such separate existence as mind distinct from matter. If this question be determined in the negative, it would appear, at first sight, that no division can be made, that there is no room for any science separate from that which treats of the laws and properties of bodies. Yet the subject is not really affected by the determination of this doubt. Every one is conscious of thinking, reasoning, willing, — of pleasure, love, and hatred; and these qualities or phenomena are wholly unlike bulk, figure, extension, and other qualities usually attributed to matter. Now we do not need to assume, in the outset, that there is a separate existence, or entity, in which the first class of these attributes inhere. There is no doubt that the two sets of phenomena are perfectly distinct from each other; there is no danger of confounding them. Avoiding all hypotheses and mooted questions, therefore, it may be said that psychology, treating of those facts which we learn from consciousness, is a branch of physical science, the other subdivisions of which relate to those facts which come to our knowledge through the senses. But it is certainly no part of psychological inquiry to seek after the origin of our notion of cause, or to analyze our idea of infinity. Observation cannot aid us here. In the external world, and in the succession of our thoughts, we witness only events or changes; we observe only sequences of phenomena; and to bind together the two terms of a sequence in the relation |