299 PHILOSOPHY OF ZOOLOGY. 
The ideas on which the imagination exercises its powers 
with the greatest success, are those which the memory can 
recall with the greatest distinctness, such as those obtained 
by the aid of the sense of sight and touch. But the ideas pro- 
duced by the impressions of the other senses, such ashearing, 
taste, or smell, cannot be so readily recollected, and at best 
but obscurely ; hence the imagination cannot operate upon 
them with any degree of success. ‘The combination of the 
ideas resulting from these last impressions, with new ob- 
jects, is seldom intimate. When, in works of fiction, they 
appear to be so, it is because we deceive ourselves with the 
signs of the sensations, which we are able to combine in 
any manner we please, while we are incapable of combin- 
ing the ideas which they represent. 
By means of imagination, thus exercised on former im- 
pressions, we are able to produce new ones, in a greater 
degree, perfect or imperfect, agreeable or disagreeable, than 
any which we have ever experienced. 
But if we restrict the operations of imagination to the 
decomposition or combination of ideas which we have ac- 
tually obtained by sensation, we render doubtful its claims 
to rank as a distinct faculty of the mind, and greatly limit 
its usefulness as an mstrument m the acquisition of know- 
ledge. It is not merely a retrospective, but a prospective 
power. By the help of memory, we recall past impressions ; 
by the help of imagination, in the exercise of this second 
function, we, as it were, render future impressions present. 
It is true that these pictures of futurity are formed of the 
materials of past impressions, but they are always in a new 
state of combination with regard to time. Sometimes they 
are more disagreeable than those of the past, when the 
mind is torn with despair. In other instances, more agree- 
able, when they are generated under the cheering infiuence 
of hope. Some of the pictures of the imagination, as those 
