That the internal material sense may act of itself, it is not necessary that the exterior senses should be absolutely in a state of repose: it is sufficient if they are without exercise. Accustomed regularly to resign ourselves to repose, we do not easily fall asleep: the body and the members, softly extended, are without motion; the eyes veiled by darkness, the tranquillity of the place, and the silence of the night, render the ear useless; alike inactive are the other senses; all is at rest, though nothing is yet lulled to sleep. In this condition, when the mind is also unoccupied with ideas, the internal material sense is the only power that acts. Then is the time for chimerical images and fluttering shadows. We are awake, and yet we experience the effects of sleep. If we are in full health, the images are agreeable, the illusions are charming; but if the body is disordered or oppressed, then we see grim and hideous phantoms, which succeed each other in a manner not more whimsical than rapid. It is a magic lanthorn, a scene of chimeras, which fill the brain, when destitute of other sensations. We remember our dreams, from the same cause that we remember sensations lately experienced; and the only difference which subsists between us and brutes is, that we can distinguish what belongs to dreams, from what belongs to our real ideas or sensations; and this is a comparison, an operation of the memory, to which the idea of time extends. While brutes, who are deprived of memory, and of this power of comparison, cannot distinguish their dreams, from their real sensations. I presume, that in treating of the nature of man, I have demonstratively shewn that animals enjoy not the power of reflection. Now the understanding, which is the result of that power, may be distinguished by two different operations. The first is the capacity to compare sensations, and form ideas from them; the second is the faculty to compare ideas themselves, and form arguments or conclusions thereon: by the first we acquire particular ideas, or the knowledge of sensible objects; by the other we form general ideas, which are necessary for the comprehension of abstract truths. Neither of these faculties do the animals possess, because they are void of understanding; and to the first of these operations does the understanding of the bulk of men seem to be limited. Were all men equally capable of comparing ideas, of rendering them general, they would equally manifest their genius by new productions, always different from, and sometimes more perfect than those of others; all would enjoy the power of invention, or at least the talents for improvement. This, however, is far from being the case. Reduced to a servile imitation, the generality of men execute nothing but what they see done by others; they only think by memory, and in the same stile as others have thought, and their understanding being too confined for invention, they proceed to follow imitation.