66 With regard to the modern philosophers | throughout his speculations, as in the pas(Leibnitz and the Cartesians) whom I had sage I have already cited respecting gravicited as having maintained that the action tation, he distinctly refuses to consider as of mind upon matter, so far from being part of the order of nature any fact which the only conceivable origin of material is not explicable from the nature of its phenomena, is itself inconceivable; the physical cause. attempt to rebut this argument by assert- With regard to the Cartesians, (not Desing that the mode, not the fact, of the cartes; I did not make that mistake, action of mind on matter was represented though the reviewer of Dr. Tulloch's Essay as inconceivable, is an abuse of the privi- attributes it to me,) I take a passage almost lege of writing confidently about authors at random from Malebranche, who is the without reading them; for any knowledge best known of the Cartesians, and, though whatever of Leibnitz would have taught not the inventor of the system of Occathose who thus speak of him, that the in- sional Causes, is its principal expositor. conceivability of the mode and the im- In Part 2, chap. 3, of his Sixth Book, possibility of the thing were in his mind having first said that matter cannot have convertible expressions. What was his the power of moving itself, he proceeds famous Principle of the Sufficient Reason, to argue that neither can mind have the the very corner-stone of his Philosophy, power of moving it. Quand on examine from which the Pre-established Harmony, l'idée que l'on a de tous les esprits finis, on the doctrine of Monads, and all the opinions ne voit point de liaison nécessaire entre most characteristic of Leibnitz were corol- leur volonté et le mouvement de quelque laries? It was, that nothing exists the corps que ce soit, on voit au contraire qu'il existence of which is not capable of being n'y en a point, et qu'il n'y en peut avoir,' proved and explained à priori; the proof (there is nothing in the idea of finite and explanation in the case of contingent mind which can account for its causing facts being derived from the nature of their the motion of a body ;) "on doit aussi causes; which could not be the causes unless conclure, si on veut raisonner selon ses there was something in their nature show- lumières, qu'il n'y a aucun esprit créé qui ing them to be capable of producing those puisse remuer quelque corps que ce soit particular effects. And this "something" comme cause véritable ou principale, de which accounts for the production of phy-même que l'on a dit qu'aucun corps ne sical effects he was able to find in many se pouvait remuer soi-même:" thus the physical causes, but could not find it in idea of Mind is, according to him, as inany finite minds, which therefore he un-compatible as the idea of Matter with the hesitatingly asserted to be incapable of exercise of active force. But when, he producing any physical effects whatever. continues, we consider not a created but "On ne saurait concevoir," he says, une a Divine Mind, the case is altered; for the action réciproque de la matière et de l'in-idea of a Divine Mind includes omnipotelligence l'une sur l'autre," and there is therefore (he contends) no choice but between the Occasional Causes of the Cartesians and his own Pre-established Harmony, according to which there is no more connection between our volitions and our muscular actions than there is between two clocks which are wound up to strike at the same instant. But he felt no similar difficulty as to physical causes; and fatality, and in any case do not appear to tence; and the idea of omnipotence does contain the idea of being able to move bodies. Thus it is the nature of omnipotence which renders the motion of bodies even by the Divine Mind credible or conceivable, while, so far as depended on the mere nature of mind, it would have been inconceivable and incredible. If Malebranche had not believed in an omnipotent being, he would have held all action of Philosophy of Creation," has returned to the point of view of Aristotle and the ancients, and vigorously reasserts the doctrine that the indication of design in the universe is not special adaptations, but Uniformity and Law, these being the evidences of mind, and not what appears to us to be a provision for our uses. While I decline to express any opinion here on this vexata quæstio, I ought not to mention Mr. Powell's volume without the acknowledgment due to the philosophic spirit which pervades generally the three Essays com. posing it, forming in the case of one of them (the "Unity of Worlds") an honourable contrast with the other dissertations, so far as they have come under my notice, which have appeared on either side of that controversy. ૨ mind on body to be a demonstrated impossibility.* A doctrine more precisely the reverse of the Volitional theory of causation cannot well be imagined. The Volitional theory is, that we know by intuition or by direct experience the action of our own mental volitions on matter; that we may hence infer all other action upon matter to be that of volition, and might thus know, without any other evidence, that matter is under the government of a divine mind. Leibnitz and the Cartesians, on the contrary, maintain that our volitions do not and cannot act upon matter, and that it is only the existence of an all-governing Being, and that Being omnipotent, which can account for the sequence between our volitions and our bodily actions. When we consider that each of these two theories, which, as theories of causation, stand at the opposite extremes of possible divergence from one another, invokes not only as its evidence, but as its sole evidence, the absolute inconceivability of any theory but itself, we are enabled to measure the worth of this kind of evidence; and when we find the Volitional theory entirely built upon the assertion that by our mental constitution we are compelled to recognise our volitions as efficient causes, and then find other thinkers maintaining that we know that they are not and cannot be such causes, and cannot conceive them to be so, I think we have a right to say that this supposed law of our mental constitution does not exist. Dr.Tulloch (pp. 45-47)thinksita sufficient answer to this that Leibnitz and the Cartesians were Theists, and believed the will tence, which renders all things conceivable, can alone take away the impossibility. This I thought, and think, a conclusive answer to the argument on which this theory of causation avowedly depends. But I certainly did not imagine that Theism was bound up with that theory; nor expected to be charged with denying Leibnitz and the Cartesians to be Theists because I denied that they held the theory CHAPTER VI. ON THE COMPOSITION OF CAUSES. of causation on which the rules of ex§ I. To complete the general notion perimental inquiry into the laws of nature must be founded, one distinction still remains to be pointed out: a distinction so radical, and of so much importance, as to require a chapter to itself. The preceding discussions have rendered us familiar with the case in which several agents, or causes, concur as conditions to the production of an effect; a case, in truth, almost universal, there being very few effects to the production of which no more than one agent contributes. Suppose, then, of God to be an efficient cause. Doubtless that two different agents, operating they did, and the Cartesians even believed jointly, are followed, under a certain (though Leibnitz did not) that it is the only set of collateral conditions, by a given such cause. Dr. Tulloch mistakes the nature of the question. I was not writing effect. If either of these agents, inon Theism, as Dr. Tulloch is, but against a stead of being joined with the other, particular theory of causation, which, if it had operated alone, under the same be unfounded, can give no effective support to Theism or to anything else. I found it set of conditions in all other respects, asserted that volition is the only efficient some effect would probably have folcause, on the ground that no other efficient lowed; which would have been diffecause is conceivable. To this assertion I rent from the joint effect of the two, oppose the instances of Leibnitz and of the Cartesians, who affirmed with equal posi- and more or less dissimilar to it. Now, tiveness that volition as an efficient cause if we happen to know what would be is itself not conceivable, and that omnipo- the effect of each cause when acting separately from the other, we are often able to arrive deductively, or à priori, at a correct prediction of what will arise from their conjunct agency. To render this possible, it is only necessary that the same law which expresses the effect of each cause acting by itself shall also correctly express the part due to that cause of the effect which follows from the two together, * In the words of Fontenelle, another celebrated Cartesian, "Les philosophes aussi bien que le peuple avaient cru que l'âme et le corps agissaient réellement et physiquement l'un sur l'autre. Descartes vint, qui prouva que leur nature ne permettait point cette sorte de communication véritable, et qu'ils n'en pouvaient avoir qu'une apparente, dont Dieu était le Médiateur."-Euvres de Fontenelle, ed. 1767, tom. V. p. 534. This condition is realised in the ex- | rately, because they continue to obtensive and important class of pheno- serve the same laws when in combinamena commonly called mechanical, tion which they observed when sepanamely, the phenomena of the com-rate: whatever would have happened munication of motion (or of pressure, in consequence of each cause taken by which is tendency to motion) from itself, happens when they are together, one body to another. In this impor- and we have only to cast up the tant class of cases of causation, one results. Not so in the phenomena cause never, properly speaking, defeats which are the peculiar subject of the or frustrates another; both have their science of chemistry. There, most of full effect. If a body is propelled in the uniformities to which the causes two directions by two forces, one tend- conformed when separate cease altoing to drive it to the north and the gether when they are conjoined; and other to the east, it is caused to move we are not, at least in the present in a given time exactly as far in both state of our knowledge, able to foredirections as the two forces would see what result will follow from any separately have carried it; and is left new combination, until we have tried precisely where it would have arrived the specific experiment. if it had been acted upon first by one of the two forces, and afterwards by the other. This law of nature is called, in dynamics, the principle of the Composition of Forces: and, in imitation of that well-chosen expres-ordinary new uniformities arise which sion, I shall give the name of the Composition of Causes to the principle which is exemplified in all cases in which the joint effect of several causes is identical with the sum of their separate effects. If this be true of chemical combinations, it is still more true of those far more complex combinations of elements which constitute organised bodies, and in which those extra are called the laws of life. All organised bodies are composed of parts similar to those composing inorganic nature, and which have even themselves existed in an inorganic state; but the phenomena of life which result from the juxtaposition of those parts in a certain manner bear no analogy to any of the effects which would be produced by the action of the component substances considered as mere physical agents. To whatever degree we might imagine our knowledge of the properties of the several ingredients of a living body to be extended and perfected, it is certain that no mere summing up of the separate actions of those elements will ever amount to the action of the living body itself. The tongue, for instance, is, like all other parts of the animal This principle, however, by no means prevails in all departments of the field of nature. The chemical combination of two substances produces, as is well known, a third substance with properties different from those of either of the two substances separately, or of both of them taken together. Not a trace of the properties of hydrogen or of oxygen is observable in those of their compound, water. The taste of sugar of lead is not the sum of the tastes of its component elements, acetic acid and lead or its oxide; nor is the colour of blue vitriol a mixture of the colours of sul-frame, composed of gelatine, fibrin, phuric acid and copper. This explains why mechanics is a deductive or demonstrative science, and chemistry not. In the one, we can compute the effects of combinations of causes, whether real or hypothetical, from the laws which we know to govern those causes when acting sepa and other products of the chemistry of digestion, but from no knowledge of the properties of those substances could we ever predict that it could taste, unless gelatine or fibrin could themselves taste; for no elementary fact can be in the conclusion which was not in the premises, There are thus two different modes of the conjunct action of causes, from which arise two modes of conflict, or mutual interference, between laws of nature. Suppose, at a given point of time and space, two or more causes, which, if they acted separately, would produce effects contrary, or at least conflicting with each other, one of them tending to undo, wholly or partially, what the other tends to do. Thus, the expansive force of the gases generated by the ignition of gunpowder tends to project a bullet towards the sky, while its gravity tends to make it fall to the ground. A stream running into a reservoir at one end tends to fill it higher and higher, while a drain at the other extremity tends to empty it. Now, in such cases as these, even if the two causes which are in joint action exactly annul one another, still the laws of both are fulfilled: the effect is the same as if the drain had been open for half an hour first,* and the stream had flowed in for as long afterwards. Each agent produced the same amount of effect as if it had acted separately, though the contrary effect which was taking place during the same time obliterated it as fast as it was produced. Here then are two causes, producing by their joint operation an effect which at first seems quite dissimilar to those which they produce separately, but which on examination proves to be really the sum of those separate effects. It will be noticed that we here enlarge the idea of the sum of two effects, so as to include what is commonly called their difference, but which is in reality the result of the addition of opposites; a conception to which mankind are indebted for that admirable extension *I omit, for simplicity, to take into account the effect in this latter case of the diminution of pressure, in diminishing the flow of water through the drain; which evidently in no way affects the truth or applicability of the principle, since when the two causes act simultaneously the conditions of that diminution of pressure do not arise, of the algebraical calculus which has so vastly increased its powers as an instrument of discovery, by introducing into its reasonings (with the sign of subtraction prefixed, and under the name of Negative Quantities) every description whatever of positive phenomena, provided they are of such a quality in reference to those previously introduced, that to add the one is equivalent to subtracting an equal quantity of the other. There is, then, one mode of the mutual interference of laws of nature, in which, even when the concurrent causes annihilate each other's effects, each exerts its full efficacy according to its own law-its law as a separate agent. But in the other description of cases, the agencies which are brought together cease entirely, and a totally different set of phenomena arise as in the experiment of two liquids which, when mixed in certain proportions, instantly become, not a larger amount of liquid, but a solid mass. § 2. This difference between the case in which the joint effect of causes is the sum of their separate effects, and the case in which it is heterogeneous to them; between laws which work together without alteration, and laws which, when called upon to work together, cease and give place to others; is one of the fundamental distinctions in nature. The former case, that of the Composition of Causes, is the general one; the other is always special and exceptional. There are no objects which do not, as to some of their phenomena, obey the principle of the Composition of Causes; none that have not some laws which are rigidly fulfilled in every combination into which the objects enter. The weight of a body, for instance, is a property which it retains in all the combinations in which it is placed. The weight of a chemical compound, the sum of the weights of the eleor of an organised body, is equal to ments which compose it, The weight either of the elements or of the combinations. The Laws of Life will pound will vary, if they be carried never be deducible from the mere farther from their centre of attraction, laws of the ingredients, but the proor brought nearer to it; but whatever digiously complex Facts of Life may affects the one affects the other. They all be deducible from comparatively always remain precisely equal. So simple laws of life; which laws (deagain, the component parts of a pending indeed on combinations, but on vegetable or animal substance do not comparatively simple combinations, of lose their mechanical and chemical antecedents) may, in more complex cirproperties as separate agents, when, cumstances, be strictly compounded by a peculiar mode of juxtaposition, with one another, and with the physical they, as an aggregate whole, acquire and chemical laws of the ingredients. physiological or vital properties in The details of the vital phenomena, even addition. Those bodies continue, as now, afford innumerable exemplificabefore, to obey mechanical and chemi- tions of the Composition of Causes; and cal laws, in so far as the operation of in proportion as these phenomena are those laws is not counteracted by the more accurately studied, there appears new laws which govern them as more reason to believe that the same organised beings. When, in short, a laws which operate in the simpler concurrence of causes takes place combinations of circumstances, do, in which calls into action new laws fact, continue to be observed in the bearing no analogy to any that we more complex. This will be found can trace in the separate operation of equally true in the phenomena of the causes, the new laws, while they mind; and even in social and political supersede one portion of the previous phenomena, the results of the laws of laws, may co-exist with another por- mind. It is in the case of chemical tion, and may even compound the effect phenomena that the least progress of those previous laws with their own. has yet been made in bringing the Again, laws which were themselves special laws under general ones from generated in the second mode, may which they may be deduced; but generate others in the first. Though there are even in chemistry many there are laws which, like those of circumstances to encourage the hope chemistry and physiology, owe their that such general laws will hereafter existence to a breach of the principle be discovered. The different actions of Composition of Causes, it does not of a chemical compound will never, follow that these peculiar, or, as they undoubtedly, be found to be the sums might be termed, heteropathic laws, of the actions of its separate elements; are not capable of composition with but there may exist, between the proone another. The causes which by perties of the compound and those of one combination have had their laws its elements, some constant relation, altered, may carry their new laws which, if discoverable by a sufficient with them unaltered into their ulterior induction, would enable us to foresee combinations. And hence there is no the sort of compound which will result reason to despair of ultimately raising from a new combination before we chemistry and physiology to the con- have actually tried it, and to judge of dition of deductive sciences; for though what sort of elements some new subit is impossible to deduce all chemical stance is compounded before we have and physiological truths from the laws analysed it. The law of definite proor properties of simple substances or portions, first discovered in its full elementary agents, they may possibly generality by Dalton, is a complete be deducible from laws which com- solution of this problem in one, though mence when these elementary agents but a secondary aspect, that of quanare brought together into some mode-tity: and in respect to quality, we rate number of not very complex com- have already some partial generalisa |