and the discovery of new ones will affect the calculations and conduct of men just as much as ever. To return to the examples first given, we do not know that the spark was the cause of the explosion, or that taking poison produced death; but we do know that the two events are always united, that one is the invariable consequent of the other, and this is enough to direct us in action. Experience loses none of its value as a trustworthy guide of life, though it is deprived of some of its factitious importance as a source of knowledge. The discovery of invari-` able sequences, of regularity in the succession of events, is the true aim of physical science. To distinguish accidental, and therefore infrequent, conjunctions from such as are constant, to separate the casual proximity in time of two events from their permanent relation to each other as antecedent and consequent, is the only object of the inquirer. An eclipse of the sun may be followed by a pestilence; a troubled dream may very soon be succeeded by some great domestic misfortune. But a brief experience of eclipses and of dreams will satisfy us, that there is no permanent relation between these two events, nothing but a fortuitous conjunction of them. On the other hand, the application of heat is always followed by the boiling of the water, and the sensation of coldness never fails to result, if the warm hand be placed upon ice. Permanent sequences are thus distinguished. from casual ones; but of the true relations of the two events to each other, of the reason or cause of their proximity, we are just as ignorant in the latter case as in the former. Previously to all experience, we have no more reason for supposing that powdered sugar will dissolve in water, and powdered marble will not, than for believing that an eclipse of the sun will be followed by an earthquake. To distinguish invariable sequences from necessary connections, Dugald Stewart and others have proposed to call the former physical causes, and the latter efficient causes. This nomenclature is good enough in one respect, as the former are the only objects of physical inquiry; but it is faulty in so far as it connects the idea of cause in any manner whatever with such relations. Physical causes, as they are termed, are only the constant forerunners and signs of certain natural events; the word cause is almost universally understood to mean nothing but efficient cause. To show both the importance and the difficulty of distinguishing invariable sequences from accidental and unessential conjunctions, I borrow an illustration from Mr. Stewart. "Let us suppose that a savage, who, in a particular instance, had found himself relieved of some bodily indisposition by a draught of cold water, is a second time afflicted with a similar disorder, and is desirous to repeat the same remedy. With the limited degree of experience which we have supposed him to possess, it would be impossible for the acutest philosopher in his situation to determine whether the cure was owing to the water which was drunk, to the cup in which it was contained, to the fountain. from which it was taken, to the particular day of the month, or to the particular age of the moon. In order, therefore, to insure the success of the remedy, he will very naturally, and very wisely, copy, as far as he can recollect, every circumstance which accompanied the first application of it. He will make use of the same cup, draw the water from the same fountain, hold his body in the same posture, and turn his face in the same direction; and thus all the accidental circumstances in which the first experiment was made will come to be associated equally in his mind with the effect produced."* The man of science, Mr. Stewart might have added, will repeat the experiment a number of times, leaving out at each trial one of the attendant circumstances, till he falls upon one, after the omission of which the desired result no longer follows. He is then popularly said to have found out the cause of the cure; but his reason for believing in the efficacy of this one antecedent, in its necessary connection with the result, is precisely the same that the savage had for believing in the necessity of all the attendant circumstances;-namely, that the application was made, * Philosophy of the Human Mind, I. 262. and the cure followed. And were he to repeat the experiment a thousand times, he could learn no more than this, the invariable attendance of one event upon the other. Why the cure takes place, he knows not. Lest I should be accused of taking an extreme case from so imperfect a science as medicine, let me say that the power of water to slake one's thirst is ascertained in precisely the same manner. After the draught, we feel no longer thirsty; and this succession of the one event to the other is all that we know about it. I pass now to a consideration of an error in the theory of causation of precisely the opposite character to that which has thus far occupied our attention. So evident does it appear to some philosophers that we never discern any efficient causes in nature, that they deny our having any knowledge of them, or any conception of their existence. The word cause, they say, whether it be called efficient or not, means nothing but invariable antecedence. The idea of efficiency, of power, of energy, is a' mere figment of the brain; it denotes nothing but constancy of succession. Dr. Brown's words are, "We give the name [cause] to that which has always been followed by a certain event, is followed by a certain event, and, according to our belief, will continue to be followed by that event, as its immediate consequent; and causation, power, or any other synonymous words which we may use, express nothing more than this permanent relation of that which has preceded to that which has followed." So well satisfied was he of the truth of this doctrine, that he said his elaborate argument in favor of it appeared to him very much like an attempt to prove the correctness of the multiplication-table. Hume and Brown are followed in this respect by Mr. Mill, who denies that we have any notion whatever of power or force apart from the substances or events in which they are supposed to inhere; he says that "there is nothing in causation but invariable, certain, and unconditional sequence," and that "reason repudiates," though the imagination may retain, the idea of some more intimate connection, of some peculiar tie, or mysterious constraint exercised by the antecedent over ירץ the consequent." He even denies the universality and necessity Against skepticism so extravagant as this, it is only necessary to adduce the fact of which I reminded you at the beginning of this Lecture, that the popular significance of the word cause is the scientific and metaphysical meaning of it, the idea being that of efficient cause, and not merely of a constant forerunner or sign of any event. I appeal to the consciousness of every one who hears me, if, by the relation of cause and effect, he does not understand a fixed and essential relation, one perfectly distinct from that of mere succession, the former event being necessarily followed by the latter, and the existence of the latter being inconceivable except as both preceded and produced by its antecedent. When you say that the falling of a spark caused the explosion, you mean something very different from the mere proximity of two successive strokes upon a bell. The idea of power, or force, is perfectly clear and distinct in your mind; I ask not now how it came there, whether it be legitimately acquired, or a mere figment of the imagination; but IT THERE, as distinguishable from all your other notions as the idea of unity, or of self. "What convinces me," says Dr. Reid, "that I have an idea of power is, that I am conscious that I know what I mean by that word, and, while I have this consciousness, I disdain equally to hear arguments for or against my having such an idea." As the idea is not complex, it cannot be analyzed, and is therefore indefinable; but in this respect it is only on the same footing with all other simple conceptions. Observe, now, to what point the discussion has brought us; to the acknowledgment that the idea of power, or efficient cause, is one of the simplest and most familiar conceptions of the hu IS man mind, yet that we can find no reality corresponding to it in the outward universe. Every change, every phenomenon, which begins to exist, must have an efficient cause; we can no more question this proposition than we can deny the axioms of the geometer. But the closest observation, the most refined analysis, nowhere discovers such a cause in the external world; it detects nothing, it never can detect any thing, but invariable antecedence, a relation which differs from that of cause as widely as the idea of person, or self, differs from that of material substance. Whence came the idea, then? Why do we suppose the existence of such a cause, or attribute to it every outward phenomenon, when it is nowhere dicoverable ? This is the problem which we must now undertake to solve. Two answers are possible to this inquiry. One is, that the idea of cause is a conception of pure reason; an original and spontaneous intuition of the soul; not furnished by experience, though first developed on occasion of its exercise; a part of the primitive constitution of the human mind; in short, an innate idea. Those to whom this answer is satisfactory, of course, need go no farther. The existence of such primitive ideas is a mere dogmatic assertion, admitted to be incapable of proof, and affirmed to be in no need of it, but to occupy a position above all argument. No inquiry into their origin, or genesis, is possible, for they had no origin, except with the birth of the mind. itself; no process of legitimating them, or establishing their objective validity, is required, as they constitute the grounds of reasoning about other things, and so cannot themselves be reasoned about. If you deny the existence of them, you are a skeptic, or a materialist, and there's an end of the matter. Now, for the purposes of this inquiry, I do not feel concerned either to affirm or deny them. Those who believe in them, as I have said, need go no farther; the conclusion to which they have come is perfectly satisfactory, though they have jumped to it; and I freely concede this point, that the idea of cause has a v better claim to be considered original and spontaneous than any other. If there are any innate ideas, this surely is one. Those |