he beginning of this treatise, that all ideas
are borrowed from impressions, and that these two kinds of perceptions
differ only in the degrees of force and vivacity, with which they
strike upon the soul. The component part of ideas and impressions are
precisely alike. The manner and order of their appearance may be the
same. The different degrees of their force and vivacity are, therefore,
the only particulars, that distinguish them: And as this difference may
be removed, in some measure, by a relation betwixt the impressions and
ideas, it is no wonder an idea of a sentiment or passion, may by this
means be inlivened as to become the very sentiment or passion. The
lively idea of any object always approaches is impression; and it
is certain we may feel sickness and pain from the mere force of
imagination, and make a malady real by often thinking of it. But this
is most remarkable in the opinions and affections; and it is there
principally that a lively idea is converted into an impression. Our
affections depend more upon ourselves, and the internal operations of
the mind, than any other impressions; for which reason they arise more
naturally from the imagination, and from every lively idea we form of
them. This is the nature and cause of sympathy; and it is after this
manner we enter so deep into the opinions and affections of others,
whenever we discover them.

What is principally remarkable in this whole affair is the strong
confirmation these phaenomena give to the foregoing system concerning
the understanding, and consequently to the present one concerning the
passions; since these are analogous to each other. It is indeed evident,
that when we sympathize with the passions and sentiments of others,
these movements appear at first in our mind as mere ideas, and are
conceived to belong to another person, as we conceive any other matter
of fact. It is also evident, that the ideas of the affections of others
are converted into the very impressions they represent, and that the
passions arise in conformity to the images we form of them. All this is
an object of the plainest experience, and depends not on any hypothesis
of philosophy. That science can only be admitted to explain the
phaenomena; though at the same time it must be confest, they are so
clear of themselves, that there is but little occasion to employ it. For
besides the relation of cause and effect, by which we are convinced of
the reality of the passion, with