shew how we can form an idea of a triangle,
for instance, which shall neither be an isoceles nor scalenum, nor be
confined to any particular length and proportion of sides. It is easy to
see, why philosophers are so fond of this notion of some spiritual
and refined perceptions; since by that means they cover many of their
absurdities, and may refuse to submit to the decisions of clear ideas,
by appealing to such as are obscure and uncertain. But to destroy this
artifice, we need but reflect on that principle so oft insisted on, that
all our ideas are copyed from our impressions. For from thence we may
immediately conclude, that since all impressions are clear and precise,
the ideas, which are copyed from them, must be of the same nature, and
can never, but from our fault, contain any thing so dark and intricate.
An idea is by its very nature weaker and fainter than an impression;
but being in every other respect the same, cannot imply any very great
mystery. If its weakness render it obscure, it is our business to
remedy that defect, as much as possible, by keeping the idea steady and
precise; and till we have done so, it is in vain to pretend to reasoning
and philosophy.

SECT. II. OF PROBABILITY, AND OF THE IDEA OF CAUSE AND EFFECT.

This is all I think necessary to observe concerning those four
relations, which are the foundation of science; but as to the other
three, which depend not upon the idea, and may be absent or present
even while that remains the same, it will be proper to explain them more
particularly. These three relations are identity, the situations in time
and place, and causation.

All kinds of reasoning consist in nothing but a comparison, and a
discovery of those relations, either constant or inconstant, which two
or more objects bear to each other. This comparison we may make, either
when both the objects are present to the senses, or when neither of them
is present, or when only one. When both the objects are present to the
senses along with the relation, we call this perception rather than
reasoning; nor is there in this case any exercise of the thought, or
any action, properly speaking, but a mere passive admission of the
impressions through the organs of sensation. According to this way of
thinking, we ought not to receive as reasoning any of the observations
we may make concerning identity, and the relations of time and place;
since in none of them the mind can go beyond what is imm