efore be easy for us to discover these qualities by a comparison
of the impressions, to which we attribute a distinct and continued
existence, with those, which we regard as internal and perishing.

We may observe, then, that it is neither upon account of the
involuntariness of certain impressions, as is commonly supposed, nor of
their superior force and violence, that we attribute to them a reality,
and continued existence, which we refuse to others, that are voluntary
or feeble. For it is evident our pains and pleasures, our passions and
affections, which we never suppose to have any existence beyond our
perception, operate with greater violence, and are equally involuntary,
as the impressions of figure and extension, colour and sound, which we
suppose to be permanent beings. The heat of a fire, when moderate, is
supposed to exist in the fire; but the pain, which it causes upon a near
approach, is not taken to have any being, except in the perception.

These vulgar opinions, then, being rejected, we must search for some
other hypothesis, by which we may discover those peculiar qualities
in our impressions, which makes us attribute to them a distinct and
continued existence.

After a little examination, we shall find, that all those objects, to
which we attribute a continued existence, have a peculiar constancy,
which distinguishes them from the impressions, whose existence depends
upon our perception. Those mountains, and houses, and trees, which lie
at present under my eye, have always appeared to me in the same order;
and when I lose sight of them by shutting my eyes or turning my head, I
soon after find them return upon me without the least alteration. My bed
and table, my books and papers, present themselves in the same uniform
manner, and change not upon account of any interruption in my seeing
or perceivilng them. This is the case with all the impressions, whose
objects are supposed to have an external existence; and is the case
with no other impressions, whether gentle or violent, voluntary or
involuntary.

This constancy, however, is not so perfect as not to admit of very
considerable exceptions. Bodies often change their position and
qualities, and after a little absence or interruption may become hardly
knowable. But here it is observable, that even in these changes they
preserve a coherence, and have a regular dependence on each other; which
is the foundation of a kind of reasoning from causation, and pr