CH. IV.] SUBSTITUTION OF NERVE- ACTIONS. 297 



their exciting cause, namely, the conceptions of the mind, and 

 in connection with the order in which they are developed, and 

 succeed each other, we find there are two kinds : 



i. Certain conceptions, namely, the sensational, are induced 

 in the mind by external impressions corporeally and necessarily 

 (65, 66), and are developed by the mind, so as to succeed 

 each other only in the same order as the external impressions 

 succeed each other, and determine the conceptions to act, 

 according to the laws of the vis nervosa. These sensational 

 conceptions are — the external sensations, imaginations, fore- 

 seeings, &c. — the sensational incitements they contain, and the 

 sensational desires and aversions, particularly the instincts 

 and passions. External sensations, together with sensational 

 pleasure and pain (80), and the blind instincts (263), are the 

 most directly induced of all these by external impressions, and 

 are developed and succeed each other just as the impressions 

 succeed each other, according to the laws of the vis nervosa, and 

 develop their material ideas in the brain; and the sentient 

 actions of these sensational conceptions are also developed in 

 like manner, (542, 543, 547, 552, &c.) The remaining sensa- 

 tional conceptions, incitements, and desires, namely, the 

 imaginations, foreseeings, &c., with their sensational pleasure 

 and pain (66, 80), and the passions (305), are somewhat more 

 free from the natural and necessary influence of external im- 

 pressions, and are developed and succeed each other more 

 according to psychological laws ; nevertheless they are not to be 

 confounded with recollections, expectations, &c. (238 249), 

 considered as simply imperfect external sensations, and not 

 directly dependent on external impressions. Hence the sentient 

 actions of imaginations, foreseeings, &c., are in fact those of the 

 external sensations to which they are related (237, 247), and as 

 such (as experience teaches) may be induced by the vis nervosa 

 only (545, 547). It is only the sentient actions of the higher 

 passions, and of the higher sensational desires and aversions, 

 which are formed and developed rather according to psycho- 

 logical laws than the laws of the vis nervosa, and which cannot 

 be induced by it as nerve-actions (573). 



ii. The other class of conceptions is the intellectual. This 

 comprises those perceptions which are not sensational, the 

 motives they contain, and the desires, aversions, and satisfactions 



