LAW OF CAUSATION. 245 



horizon. If the sun ceased to rise, which, for aught we know, may be per- 

 fectly compatible with the general laws of matter, night would be, or might 

 be, eternal. On the other hand, if the sun is above the horizon, his light 

 not extinct, and no opaque body between us and him, we believe firmly that 

 unless a change takes place in the properties of matter, this combination of 

 antecedents will be followed by the consequent, day; that if the combina- 

 tion of antecedents could be indefinitely pi'olonged, it would be always day ; 

 and that if the same combination had always existed, it would always have 

 been day, quite independently of night as a previous condition. Therefore 

 is it that we do not call night the cause, nor even a condition, of day. The 

 existence of the sun (or some such luminous body), and there being no 

 opaque medium in a straight line* between that body and the part of the 

 earth where we are situated, are the sole conditions ; and the union of 

 these, without the addition of any superfluous circiamstance, constitutes the 

 cause. This is what writers mean when they say that the notion of cause 

 involves the idea of necessity. If there be any meaning which confessedly 

 belongs to the term necessity, it is uncoiiditionalness. That which is nec- 

 essary, that which niiist be, means that which will be, whatever supposition 

 we may make in regard to all other things. The succession of day and 

 night evidently is not necessary in this sense. It is conditional on the oc- 

 currence of other antecedents. That which will be followed by a given 

 consequent when, and only when, some third circumstance also exists, is not 

 the cause, even though no case should ever have occurred in which the phe- 

 nomenon took place without it. 



Invariable sequence, therefore, is not synonymous with causation, unless 

 the sequence, besides being invariable, is unconditional. There are se- 

 quences, as uniform in past experience as any others whatever, which yet 

 we do not regard as cases of causation, but as conjunctions in some sort 

 accidental. Such, to an accurate thinker, is that of day and night. The one 

 might have existed for any length of time, and the other not have followed 

 the sooner for its existence; it follows only if certain other antecedents 

 exist ; and Avhere those antecedents existed, it would follow in any case. 

 No one, probably, ever called night the cause of day ; mankind must so 

 soon have arrived at the very obvious generalization, that the state of gen- 

 eral illumination which we call day would follow from the presence of a 

 sufficiently luminous body, whether darkness had preceded or not. 



We may define, therefore, the cause of a phenomenon, to be the ante- 

 cedent, or the concurrence of antecedents, on which it is invariably and 

 imconcUtionally consequent. Or if we adopt the convenient modification 

 of the meaning of the word cause, which confines it to the assemblage of 

 positive conditions Avithout the negative, then instead of "unconditional- 

 ly," we must say, " subject to no other than negative conditions." 



To some it may appear, that the sequence between night and day being 

 invariable in our experience, we have as much ground in this case as ex- 

 perience can give in any case, for recognizing the two phenomena as cause 

 and effect ; and that to say that more is necessary — to require a belief that 

 the succession is unconditional, or, in other words, that it would be invari- 

 able under all changes of circumstances, is to acknowledge in causation an 



* I use the words "straight line" for hrevity and simplicity. In reality the line in question 

 is not exactly straight, for, from the effect of refraction, we actually see the sun for a short 

 interval during which the opaque mass of the earth is interposed in a direct line between the 

 sun and our eyes ; thus realizing, though but to a limited extent, the coveted desideratum of 

 seeing round a corner. 



