It

Sir John Herschel argues that "all bodies, when raised into the air and quietly abandoned, descend to the earth's surface in lines perpendicular to it. They are therefore urged thereto by a force or effort, the direct or indirect result of a consciousness and a will existing somewhere, though beyond our power to trace, which force we term gravity." This is in every way objectionable. creates the fiction of an Efficiens which is not Materia, a Will apart from all the known conditions, and supposes that the material changes we observe are the products of this immaterial Efficiens. And even then it disregards the specialty of the facts. Unless we mean by cause something wholly unallied to consequent effect, something which is prior to, but not procreant of, the effect, we can no more assign gravity to will than we can assign the death of a man to the flash of the explosion which preceded it.

* HERSCHEL, Outlines of Astronomy, 1849, Chap. VII.

CHAPTER III.

THE IDENTITY OF CAUSE AND EFFECT.

58. THROUGHOUT the preceding chapter we have endeavored to make clear that the terms cause and effect are simply different expressions of identical processes viewed under different aspects. It will now be needful to consider certain objections which may naturally arise in the reader's mind when he thinks of the obvious unlikeness between causes and effects, and of the facts which seem to imply that one and the same cause may have very different effects, and that two or more very different causes may have the same effect.

Nothing is commoner than to hear the same cause assigned to different effects; but in such cases the supposed cause is simply one conspicuous agent in a group. of agents, and when it is wrested from this group, and introduced into some other group, the result is necessarily different. It is by no variation in arithmetical laws that because 5 added to 3 yields 8, the addition of 5 to 7 yields 12, and not 8. It is by no variation in causation that a mutton-chop which would have been excellent food an hour ago, will now be an injurious burden to the organism. When we see the same agent, say Electricity, producing different effects on skin, tongue, ear, and eye, or on water, gas, and salts, the effects are different because the causes are different, and we are in error in assigning the effects to the single agent Electricity. 59. It was a happy stroke of identification by which

Lavoisier saw that Respiration and Combustion were both effects of oxygenation. But although oxygen is an agent in both, it is not the sole determinant. Depriving the blood of its oxygen is very similar to depriving the air of its oxygen; and, so far as this agent is concerned, there is a corresponding similarity in the two results, the respiration ceases slowly, and the flame. expires. Observe, however, the danger of Deduction, when proceeding on such an isolation of one agent as the cause. Since respiration and combustion decrease with diminution of oxygen, it is a natural inference that they would increase with increase of oxygen; and, were oxygen the cause, this inference would be correct. But what says fact? In pure oxygen the flame burns brighter, but the animal expires, that agent which renders the flame intense, renders the animal comatose.

60. If the same cause will produce different effects, different causes will produce the same effect; and this is the popular belief, founded on such facts as that both heat and cold reduce congestion. In ordinary phrase we Here the same effect results from oppo

should say, site causes,"

cold lessening the flow of blood by contracting the arteries; and heat facilitating the exit of the blood from the congested region by dilating the arteries.* Again, the beating of the heart may be made to cease by irritation of the vagus, - by irritation of the nerves of the trunk, — by repeated light taps on the stomach, — by an emotion of terror or of joy. These various antecedents are, however, not various causes, but various movements which may liberate the energy of one determinant, precisely as the various modes of magnetizing an iron rod by rubbing it with a magnet, hammering it in the direction of the magnetic line, or winding an electrical coil round

*Hence the application of cold is most efficient in the early stages, acting as a preventive; and heat in the later stages, acting as a curative.

it, are operative through one determinant, which is therefore one cause with various accompaniments not causal, i. e. not passing into the effect. Asphyxia is an effect which may succeed various antecedent events, but proceeds only from one cause. The antecedent events may be submersion under water, tying a cord round the neck, vitiation of the atmosphere by overdose of carbonic acid, or by a small dose of carbonic oxide, etc.; but it is not the submersion, the water, the cord, nor the gases which are the efficient causes. The efficient cause, or determinant, is the arrested function of the nerve centres, an arrest due to the prevention of the requisite supply of oxygenated blood. The carbonic acid and the carbonic oxide by their presence prevent the blood being renovated by oxygen; the cord and the water prevent this also.

61. The identity of cause and effect, under their diversity of aspect, is like the identity of the curve under its convex and concave aspects. J. R. Mayer has well said: "Forces are causes, consequently herein there is a perfect application of the principle, causa æquat effectum. If the cause c has the effect e, then is c=e; if, again, e is the cause of another effect, f, then is e=ƒ, and so on. Thus not only does ce, but c=f, since ce=f; and reversely fc. If a given cause has produced an effect equal to itself, it has necessarily in that very production ceased to be what it was, and has passed into what it has become. Otherwise there would have been a creation out of nothing; for the cause would still exist as cause, and the effect would have been produced without absorbing the cause; c would not then =e. Again, if after the production of the effect there still remained any portion of the cause unabsorbed, there would then be further effects producible by this remaining portion, and thus the total effect of c would be greater than e, which would be

* MAYER, Die Mechanik, der Wärme, p. 3.

a contradiction of c=e. "Hence," continues Mayer, 'since c becomes e, and e becomes f, etc., we must consider these magnitudes as different phenomenal forms of one and the same object. As the first property of causes is indestructibility, the second property is convertibility, or capability of assuming various forms." But this assumption of various forms must not be understood in the sense of a metamorphosis; - each cause is invariant, but its combining relations are variable. No agent changes itself, it only enters into new relations with others. This is the meaning of the quantitative indestructibility and the qualitative convertibility of forces and causes.

62. When the case is stated in this abstract form, and the equation of cause and effect is seen to be self-evident, the reader may not only free his mind from all the ancient difficulties respecting the connection of cause and effect, the unlikeness of effects to their causes, and the variety of effects following from the same cause; but he may also ask how it is that these questions arose to puzzle philosophers. Instead of disputing whether there is any intuitive or demonstrative ground for the belief in a necessary connection (or whether there is any objective validity in the belief), let us consider how it is that, long after philosophers had formulated the truth in such axioms as causa æquat effectum, "like causes have like effects," they could still maintain the reality of the logical distinction between cause and effect; and, having established the distinction, were forced to invent a mysterious causal link connecting the two.

HUME'S THEORY OF CAUSATION.

63. The chief source of the confusion is the ambiguity of language. No sooner do we express ourselves in the precise and abstract symbols of Mathematics, than the equation, before so obscure, becomes luminous. How