298 THE FOUNDATIONS OF ZOOLOGY 



exist, or have existed, in human minds ; nor is proof that a thing 

 exists in all human minds proof that it exists in nature outside 

 human minds. 



The " law of causation " seems to consist of two elements. 

 Our whole history as living beings gives new strength continually 

 to our confidence that, when event A, which we call a cause, 

 exists, event B, which we call its effect, may be expected ; and 

 that in the absence of A, B will not be found. The belief also 

 prevails that B cannot occur without A, and that it must occur 

 with A. 



It does not seem difficult to consider these elements separately; 

 and whatever may be our opinion of their separation in fact, the 

 analysis may help us to examine the subject. 



Every rational action is based upon our confidence that each 

 event is, in course of nature, a sign of others that may be ex- 

 pected. This confidence gathers strength with every moment of 

 our lives, and is so ingrained in our language, that we speak of 

 the sign as if it were, in very truth, the thing signified. When 

 we hear a pattering sound on the roof, we do not restrict our- 

 selves to fact, and say we hear a sound. We say we hear it 

 rain. I have tried to show that life itself, not only^ the conscious, 

 rational life of man and of the higher animals, but the life of 

 every animal and every plant, is response. A living being is a 

 being which when affected by A makes preparations to meet B. 

 The rhizopod which flows around and ingests small particles of 

 food, while it retracts its pseudopodia when violently jarred, re- 

 sponds to the law of causation as much as the sailor who corrects 

 'his chronometer by observations on the satellites of Jupiter. Re- 

 sponse to this law is admitted to be entirely organic in the lower 

 living things, and to a great extent organic in all. As man has 

 by nature structural adjustments to many of these relations be- 

 tween phenomena, the law of causation seems, to this extent, 

 embodied in his organization as part of his nature, and we have 

 already seen that, while the value of our confidence in this order 

 is measured by our experience, its intensity is not. There is no 

 constant ratio between the intensity with which a burnt child 

 dreads the fire and the number of times it has been burned. In 

 this sense the law of causation seems to be necessary, inasmuch 



