200 INTRODUCTION 



APPENDIX A. 



EXPLANATION OF THE PRE-ESTABLISHED HARMONY BY 

 A SPECIAL INSTANCE. 



IN a letter to Arnauld (1687) (G. ii. 113) Leibniz gives an 

 account of the way in which his theory may be applied to 

 a particular case (that of the relation between a pin-prick 

 in the body and pain in consciousness).. 'We have now to 

 inquire how the soul is conscious of the motions of its body, 

 since we can see no way of explaining by what channels the 

 activity of an extended mass can pass into an indivisible being. 

 Ordinary Cartesians declare that no explanation of this union 

 can be given. The authors of the hypothesis of occasional 

 causes think that it is nodus vindice dignus, cui Deus ex Machina 

 intervenire debeat. For my part I explain it in a natural way. 

 From the notion of substance or concrete [accompli] being in 

 general, which declares that its present state is always a natural 

 consequence of its preceding state, it follows that the nature of 

 each individual substance, and consequently of every soul, is to 

 express the universe. Each has been from the first created 

 such that, in virtue of the laws of its own nature, it must 

 happen that it is in harmony with what takes place in bodies, 

 and especially in its own body. We need not then be surprised 

 to find that it has the power of representing to itself the pin- 

 prick, when this takes place in its body. And, to complete my 

 explanation on this point, we have : 



State of the body at moment A. State of the soul at moment A. 



State of the body at the following State of the soul at moment B. 

 moment B. 



(Pin-prick.) (Pain.) 



1 As, then, the state of the body at moment B follows from the 

 state of the body at moment A, so the state of the soul B is 

 a consequence of A, the preceding state of the same soul, 

 according to the notion of substance in general. Now the 



