376 NEW ESSAYS 



In a word, unconscious [insensible] perceptions are of as 

 great use in pneumatics i6 as imperceptible [insensible] S1 

 corpuscles are in physics ; and it is as unreasonable to 

 reject the one as the other on the ground that they are 

 beyond the reach of our senses * 8 . Nothing takes place 

 all at once, and . it is one of my great maxims, one 

 among the most completely verified of maxims, that nature 

 never makes leaps ; which I called the Jaw of continuity 9 

 when I spoke of it in the first 90 Nouvelks de la EepuUique 

 des Lettres 91 ; and the use of this law in physics is very 

 considerable : it is to the effect that we always pass from 



held that 'colour, heat,' &c., as we perceive them, are not to be 

 attributed to external bodies, the qualities of which are all forms 

 of motion. There is on his view no absolute reason why one kind 

 of motion should produce in us the sensation of colour and another 

 the sensation of heat. Leibniz, on the other hand, regards motions 

 as themselves perceptions of a very low degree of distinctness, and 

 the unconscious perceptions which in combination give rise" to our 

 conscious sensation form a connecting link between the motions of 

 bodies and our corresponding sense-perception of their qualities. 



86 A name for the philosophy of mind or spirit, derived from the 

 New Testament use of trvfvfjLa. In Scholastic times it included 

 natural theology and the doctrines regarding angels and demons, 

 as well as 'psychology.' In the seventeenth century it was used 

 in the more limited sense by Alsted in his Encyklopadie (1630), 

 a work which, according to Diderot, Leibniz thought of re- 

 modelling, with the assistance of other scholars ((Euvres de Diderot, 

 ed. Assezat, vol. xv. p. 440). Cf. G. vii. 67. The terms Pneumaticks 

 and Pneumatology (in the sense of philosophy of the mind) were 

 used in the Scottish Universities in the end of the seventeenth 

 and beginning of the eighteenth centuries. The word Pneumatics 

 has now ceased to have any connexion with the philosophy of 

 mind and is used to describe the branch of hydrodynamics which 

 is concerned with gases. 



87 E. omits ' imperceptible [insensible'].' 



88 The reference is probably to the views of Descartes. See 

 Principia, Part iv. 201. 



89 Cf. Introduction, Part ii. p. 37 ; Part iii. p. 83. 



90 E. reads ' when I spoke of it elsewhere in the Nouvelles,' &c. 



91 This was Bayle's magazine, and Leibniz formulated his law for 

 the first time in the letter to Bayle (1687) to which reference is 

 here made. (See G. iii. 51 ; E. 104.) For a translation of this see 

 Introduction, Part iii. p. 83 note. 



