CHAPTER XXVIII.

COUNTERACTING AND COMPLEX CAUSES.

WE have reasoned thus far on the assumption that an adequate cause is invariably accompanied by its effect. We have virtually said: 'The effect may be present without this particular cause, because the same effect Counteractmay be due to any one of several causes; but ing causes. that does not imply that the cause can be present without its effect, and if what we supposed to be a cause of a given effect is ever found to be present without the effect, we were mistaken in supposing it was the cause (though it might have been part of the cause). If A causes N, N may sometimes be present without A, but A can never be present without N.' This is the principle on which we have been reasoning up to the present, and if we were in a world in which nothing else could come between ' A and N, or affect their relations to each other, reasoning based on this principle would always be correct. As it is, it is not. It may be that A is a perfectly adequate cause of N and yet that it is sometimes. present without N. In the presence of a 'Counteracting Cause' a cause perfectly adequate in itself will fail of its effect. The swift current of a river causes things floating in it to drift down the stream; and yet if there is a hurricane blowing in the opposite direction, the things may drift up and not down. The working of the engines makes the ship move; but now she is fast on the rocks and for all their work the engines cannot move her.

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Without going into any theoretical discussion, the practical lesson to draw from such cases is this: There is a difference between saying that a cause always produces its natural effects and saying that it always tends to produce them; and this latter is all we have a right to say. Put more concretely, this rule means that if we are searching for the cause of a given effect N and find that A is sometimes present when N is not, we must not conclude from this that A is not the cause of N, until we are sure that there is nothing present which can counteract A's effect.

If we know what can counteract the effect of A, or, what amounts in this case to the same thing, what can prevent the production of N, our task of discovering the relation between A and N will be easy enough. But if we do not know enough about either A or N to say what would prevent the one from causing the other, then our task will be very much more difficult. If A and N occur together often enough to make us suspect that A is really a cause of N, though sometimes counteracted in its working by G, H, or J, we must simply leave the matter doubtful until we can make or find conditions simple enough or varied enough to let us infer something about the real nature of some of these influences.

Sometimes a situation may be so complicated that we have to deal not only with several kinds of causes and counteracting causes, but with still other antecedents that counteract the counteracting causes. But however complicated our problem may be, the principle of exclusion upon which we must depend for its solution remains the same.

The possibility of counteracting causes makes it possible to commit a blunder of precisely the opposite kind from that made possible by the plurality of possible causes. If we forget that practically the same effect can be produced by any one of several causes, we may assert that something is the cause of this effect, when it is not the cause at all, simply because it happens to be the only one thing present in all

the cases we have observed. On the other hand, if we forget that a cause is sometimes counteracted, we may deny that something is the cause, when it really is, because it is sometimes present without the effect. Thus, if we are careless, the presence of a plurality of causes may make us find false causes, and the presence of a counteracting cause may make us overlook true ones.

Methods of investigating causal relations have been discussed thus far as though we assumed that every effect had some one simple cause and every cause some one simple effect. But it often happens that several pounded' or causes act together to produce a given effect and that there is some reason why we should not regard them as

one.

Causes com

combined '.

There are two ways in which causes can act together to produce a joint effect. Sometimes the effect of each one of them separately is like that of each of the others and like that of the group as a whole. Sometimes the separate effect of each is unlike the effect of each of the others, and the effect of all together is unlike the effect of any one. Here is a case of the first sort. The amount of money that a man has at the end of the year depends upon how much he had to start with, what he made or lost each day in his regular business, what he made or lost in other ways, what he spent for regular household purposes, what he spent for amusement, what he gave away. In his cash account he sets down all the expenditures on one page and all the receipts on another, adds all the items on the same page together, and subtracts them from the total of the other page. In his balance it makes absolutely no difference what the money that he spent was spent for. If he wants a certain balance and finds before the end of the year that he is spending too much for rent and groceries, he may make up for it by cutting down his expenditures for recreation and charity. All the forces dealt with in mechanics are causes of this sort. When one is added to' or 'subtracted from another the

result is precisely the same as it would have been if the body on which they are acting had been acted upon by only one force equal to the sum or the difference. In mechanics we speak of the Composition of Forces'; and Mill paraphrases the term and speaks of the Composition of Causes' when the effect of them all can be considered in this way as the algebraic sum of the effects of each of them. The separate causes and effects which are thus added together he speaks of as Compounded'.

To raise a crop

Now for the second kind of joint effects. of onions there must be seeds, air, moisture, warmth, and soil. If any one of these is left out, the result is, not smaller onions or fewer onions, but no onions at all. Moreover if a farmer finds that his onions are getting too much heat from the sun, he cannot even things up by giving them so much less water. In the same way if a cook finds that she has put too much sugar into her cake, she cannot improve matters by leaving out the flour. Cooking is a matter of chemistry, and chemistry is full of examples of this kind of joint effects. Oxygen and hydrogen combine to form water, whose appearance and action are quite different in almost every respect from those of either of them. In the same way the green poisonous gas chlorine combines' with the very different yellowish metal sodium to form common salt, which again is very different from either of them. Joint effects which differ in this way from the effects of any of the causes separately are called Heteropathic', and since the effect of uniting the causes is like that of making a chemical ' combination' the causes are said to be 'Combined'. To produce heteropathic or combined effects it is necessary that the causes concerned should all be present at the same time or follow each other in some fixed order. If the onion seed is to grow, it must be warmed and moistened after it is put in the soil, not before; if the cake is to taste right, its various ingredients must be mixed before it is cooked, not afterwards. To produce compound effects this is not

necessary. The onions weigh as much whether they are all thrown into the basket at once or one after the other; the ingredients of the cake cost as much whether they are all purchased at the same time or at different times. The parallelogram of forces' in physics is a graphic way of explaining that when a body that can move freely is acted upon by several forces at once it reaches the same point (though it travels along a diagonal) as it would have reached. if it had been acted upon by the same forces one after the other.

Because mathematics can be applied freely in calculating the joint effect when causes are compounded' but cannot be so applied when they are combined', we have made a distinct advance in knowledge when we can say beforehand in which way they will be conjoined. For example, it is a great advantage if we can be sure that the weight of a compound, however formed, is always equal to the compounded weight-i.e., to the sum of the weights-of its ingredients. According to an old story the Royal Society was once tricked into discussing the question why it was that nothing is added to the weight of a vessel of water when a live fish is put into it; and the discussion of one explanation after another went on for a long time before any one suggested that they try the experiment and see whether what they were trying to explain was really the case. The moral naturally attached to the story is that it is wise to find out whether a fact exists before you try to explain it; but here it is used to illustrate something else. If any one were quite sure that the weight of any body is a compound effect made up of the weight of all its separate parts, he would not think it necessary to try the experiment at all. He could be sure beforehand that an addition of any kind to the contents of the vessel would increase its weight, and he would know that whether the fish put into it were alive or dead could make no possible differIf the Royal Society ever did seriously discuss such a question as this, it must have been when physicists were

ence.