LOGIC. 



ourselves of all these, we are prepared to calculate 

 the effects of any combinations of them. Nature 

 rarely presents us with a cause and its effect 

 standing alone. The usual case is to have a 

 multitude of effects flowing from a multitude of 

 causes. It requires, therefore, the whole analytic 

 force of the mind to be devoted to their reduction 

 to single couples of cause and effect. 



The great object of inductive inquiry being 

 to ascertain, among a multitude of connected 

 things, which of them stand to each other in the 

 relation of cause and effect, we have now to con- 

 sider the methods of observation and experiment 

 suited to this determination. By ' experiment ' is 

 meant the process of altering the arrangements 

 presented by nature, and shaping new arrange- 

 ments of our own to assist us in ascertaining the 

 simple sequences of cause and effect. Thus, if 

 nature presented to our observation a confused 

 and complicated train, and if we contrive to 

 remove a great many of the circumstances, so as 

 to reduce the train to a more simple sequence, 

 we are said to proceed by experiment. If we 

 find or observe a certain locality is exceedingly 

 favourable to health ; and if, in our wish to 

 ascertain which of all the peculiarities of the 

 place is the cause of the wholesomeness, we 

 endeavour to put ourselves into situations where 

 each circumstance is excluded in turn, we are 

 said to proceed experimentally. Mr Mill has laid 

 down the different ways of arriving at cause and 

 effect by this experimental procedure, under the 

 title of the ' Four Experimental Methods ; ' which 

 he names the Methods of Agreement, of Differ- 

 ence, of Residues, and of Concomitant Variations. 



' The simplest and most obvious modes of sing- 

 ling out from the circumstances which precede 

 or follow a phenomenon those with which it is 

 really connected as an invariable law, are two in 

 number : one is, by comparing together different 

 instances in which the phenomenon occurs ; the 

 other is, by comparing instances in which the 

 phenomenon does occur, with instances in other 

 respects similar, in which it does not. These two 

 methods may respectively be denominated the 

 Method of Agreement, and the Method of Differ- 

 ence. 



' In illustrating these methods, it will be neces- 

 sary to bear in mind the twofold character of 

 inquiries into the laws of phenomena ; which may 

 be either inquiries into the cause of a given effect, 

 or into the effects and properties of a given cause. 



' For example, let the antecedent be the contact 

 of an alkaline substance and an oiL This com- 

 bination being tried under several varieties of 

 circumstance resembling each other in nothing 

 else, the results agree in the production of a 

 greasy and detersive or saponaceous substance. 

 It is therefore concluded that the combination 

 of an oil and an alkali causes the production of 

 soap.' 



Mr Mill states the method of Agreement in a 

 formal canon as follows : If two or more instances 

 of the phenomenon under investigation have only 

 one circumstance in common, the circumstance in 

 which alone all the instances agree is the cause (or 

 effect) of the given phenomenon. 



By the method of Difference is meant the pro- 

 cess of comparing two sets of circumstances 

 one containing the effect, and the other not ; and 

 where between the two we can see no difference 



except in one other particular. 'When a man is 

 shot through the heart, it is by this method we know 

 that it was the gunshot that killed him ; for he 

 was in the fulness of life immediately before, all 

 circumstances being the same, except the wound.' 

 This method is expressed as follows: If an 

 instance in which the phenomenon under investi- 

 gation occurs, and an instance in which it does not 

 occur, have every circumstance, except one, in 

 common, that one occurring only in the former, 

 the circumstance in which alone the two instances 

 differ is the effect, or cause, or a necessary part 

 of the cause, of the phenomenon. 



The method of residues will be seen to be 

 a carrying out of the same attempt to break up 

 complicated trains, and to fasten down the in- 

 variability of sequence upon the true particulars 

 where cause and effect operate. It is stated thus : 

 Subduct from any phenomenon such part as is 

 known by previous induction to be the effect of 

 certain antecedents, and the residue of the phenom- 

 enon is the effect of the remaining antecedents. 



( There remains a class of laws which it is im- 

 practicable to ascertain by any of the three 

 methods which I have attempted to characterise 

 namely, the laws of those permanent causes, 

 or indestructible natural agents, which it is impos- 

 sible either to exclude or to isolate, which we can 

 neither hinder from being present, nor contrive 

 that they shall be present alone.' Heat is an 

 example of this kind of agents ; we can neither 

 divest bodies of their heat, nor exhibit it by itself 

 and apart from all other things ; and hence the 

 methods above alluded to would entirely fail in 

 determining what things are connected with it as 

 cause and effect. To meet this difficulty, we have 

 recourse to a method named by Mr Mill the 

 Method of Concomitant Variations that is, in 

 such a case as Heat, we observe what effects 

 increase as it increases, and diminish as it dimin- 

 ishes. The method is expressed in general 

 terms as follows : Whatever phenomenon varies 

 in any manner whenever another phenomenon 

 varies in some particular manner, is either a 

 cause or an effect of that phenomenon, or is con- 

 nected with it through some fact of causation. We 

 very frequently proceed upon this method of 

 observing the effects of the increased or dimin- 

 ished quantity of things, in order to see what 

 effects they have a tendency to produce, judging 

 rightly that if one event be the cause of another, 

 the two will rise and fall together. 



There are two kinds of complications that are 

 beyond the reach of any of these four methods, 

 and require a distinct treatment The one is 

 termed the case of the Plurality of Causes ; the 

 other, the Intermixture of Effects. By a plurality 

 of causes is meant, that it sometimes happens 

 that an effect may arise equally from several 

 causes, creating, as it were, an ambiguity of 

 causation. Thus, a motion may arise from any 

 one of a great number of forces happiness or 

 misery is produced by innumerabe agencies. In 

 such cases, the methods above stated are some- 

 what nonplussed, inasmuch as it may be possible 

 to exclude one cause, and yet keep in another. 

 A still greater difficulty is presented by the Inter- 

 mixture of Effects that is, when an effect is not 

 single, but complex. Thus, the course of a pro- 

 jectile is not a single, but a mixed effect, or 

 two different effects combined into one different 



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