dily takes one idea for another, where their influence
on the mind is similar; hence it proceeds, that any such succession
of related qualities is readily considered as one continued object,
existing without any variation. The smooth and uninterrupted progress of
the thought, being alike in both cases, readily deceives the mind, and
makes us ascribe an identity to the changeable succession of connected
qualities.

But when we alter our method of considering the succession, and instead
of traceing it gradually through the successive points of time, survey
at once Any two distinct periods of its duration, and compare the
different conditions of the successive qualities; in that case the
variations, which were insensible when they arose gradually, do now
appear of consequence, and seem entirely to destroy the identity. By
this means there arises a kind of contrariety in our method of thinking,
from the different points of view, in which we survey the object, and
from the nearness or remoteness of those instants of time, which we
compare together. When we gradually follow an object in its successive
changes, the smooth progress of the thought makes us ascribe an identity
to the succession; because it is by a similar act of the mind we
consider an unchangeable object. When we compare its situation after
a considerable change the progress of the thought is broke; and
consequently we are presented with the idea of diversity: In order to
reconcile which contradictions the imagination is apt to feign something
unknown and invisible, which it supposes to continue the same under
all these variations; and this unintelligible something it calls a
substance, or original and first matter.

We entertain a like notion with regard to the simplicity of substances,
and from like causes. Suppose an object perfectly simple and indivisible
to be presented, along with another object, whose co-existent parts are
connected together by a strong relation, it is evident the actions of
the mind, in considering these two objects, are not very different. The
imagination conceives the simple object at once, with facility, by a
single effort of thought, without change or variation. The connexion of
parts in the compound object has almost the same effect, and so unites
the object within itself, that the fancy feels not the transition in
passing from one part to another. Hence the colour, taste, figure,
solidity, and other qualities, combined in a peach