260 An Essay on the Signs of Ideas. 
of these words is, however, both proper and 
necessary, for without them the mathemati- 
cian could not proceed.a single step, and in 
the way in which they are used they do not 
occasion any error. 
With regard to the second kind, it will be 
recollected, that in an early part of this pa- 
per, I mentioned that some of our simple and 
original sensations, as those of the eye, and 
the ear, most strongly, and those of the nose, 
and mouth, more weakly and transiently, 
were capable of recurring when the objects, 
from which they originally arose, are absent ; 
whilst the sensations of other organs and tex- 
tures, and also those sensations called emo- 
tions, are incapable of returning, without a 
fresh application of the original cause. 
Tt is evident, then, that when we are reason- 
ing concerning objects, (or, what is precisely 
the same thing, sensations,) of the two for- 
mer classes, those of sight and hearing, the 
objects themselves being absent, we are, or 
may be, actually conscious of the ideas’ to 
which they have given rise. But, with re- 
gard to the simple sensations of other organs 
and textures, and also with regard to sensa- 
tions of emotion, we generally consider, not 
the ideas, (for these we either never have at 
all, or at least, as in the case of the nose 
