of the nerves of sense, by which they were acquired; and that this belief
is not, as some late philosophers contend, an instinct necessarily
connected only with our perceptions.

7. A curious question demands our attention in this place; as we do not
distinguish in our dreams and reveries between our perceptions of external
objects, and our ideas of them in their absence, how do we distinguish them
at any time? In a dream, if the sweetness of sugar occurs to my
imagination, the whiteness and hardness of it, which were ideas usually
connected with the sweetness, immediately follow in the train; and I
believe a material lump of sugar present before my senses: but in my waking
hours, if the sweetness occurs to my imagination, the stimulus of the table
to my hand, or of the window to my eye, prevents the other ideas of the
hardness and whiteness of the sugar from succeeding; and hence I perceive
the fallacy, and disbelieve the existence of objects correspondent to those
ideas, whose tribes or trains are broken by the stimulus of other objects.
And further in our waking hours, we frequently exert our volition in
comparing present appearances with such, as we have usually observed; and
thus correct the errors of one sense by our general knowledge of nature by
intuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power of
volition is suspended, we can recollect and compare our present ideas with
none of our acquired knowledge, and are hence incapable of observing any
absurdities in them.

By this criterion we distinguish our waking from our sleeping hours, we can
voluntarily recollect our sleeping ideas, when we are awake, and compare
them with our waking ones; but we cannot in our sleep _voluntarily_
recollect our waking ideas at all.

8. The vast variety of scenery, novelty of combination, and distinctness of