The PREFACE.

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LET this also still be remembered
that the natural dispositions of man-
kind will operate regularly in those
who never reflected upon them, nor
formed accurate notions about them.
Many are really virtuous who can-
not explain what virtue is. Some
act a most generous, disinterested part
in life, who have been taught to
account for all their actions by
self-love, as their sole source.
There have been very different and
opposite opinions in optics; con-
trary accounts have been given of
hearing, voluntary motion, di-
gestion, and other natural actions.
But the powers themselves in real-
ity perform their several operations
with sufficient constancy and uni-
formity in persons of good health,
whatever their opinions be about
them. In the same manner, our
moral actions and affections may
be in good order, when our opini-