BOOK I PART III
supposition; there being in them, neither any
present impression, nor belief of a real exis-
tence.
I need not observe, that it is no just objec-
tion to the present doctrine, that we can rea-
son upon our past conclusions or principles,
without having recourse to those impressions,
from which they first arose. For even sup-
posing these impressions should be entirely ef-
faced from the memory, the conviction they
produced may still remain; and it is equally
true, that all reasonings concerning causes and
effects are originally derived from some im-
pression; in the same manner, as the assur-
ance of a demonstration proceeds always from
a comparison of ideas, though it may continue
after the comparison is forgot.