shall add as a fourth corrollary that we can never have reason to
believe that any object exists, of which we cannot form an idea. For as
all our reasonings concerning existence are derived from causation,
and as all our reasonings concerning causation are derived from
the experienced conjunction of objects, not from any reasoning or
reflection, the same experience must give us a notion of these objects,
and must remove all mystery from our conclusions. This is so evident,
that it would scarce have merited our attention, were it not to obviate
certain objections of this kind, which might arise against the following
reasonings concerning matter and substance. I need not observe, that
a full knowledge of the object is not requisite, but only of those
qualities of it, which we believe to exist.

SECT. XV. RULES BY WHICH TO JUDGE OF CAUSES AND EFFECTS.

According to the precedent doctrine, there are no objects which by the
mere survey, without consulting experience, we can determine to be the
causes of any other; and no objects, which we can certainly determine in
the same manner not to be the causes. Any thing may produce any thing.
Creation, annihilation, motion, reason, volition; all these may arise
from one another, or from any other object we can imagine. Nor will this
appear strange, if we compare two principles explained above, THAT THE
CONSTANT CONJUNCTION OF OBJECTS DETERMINES THEIR CAUSATION, AND [Part I.
Sect. 5.] THAT, PROPERTY SPEAKING, NO OBJECTS ARE CONTRARY TO EACH OTHER
BUT EXISTENCE AND NON-EXISTENCE. Where objects are not contrary,
nothing hinders them from having that constant conjunction, on which the
relation of cause and effect totally depends.

Since therefore it is possible for all objects to become causes or
effects to each other, it may be proper to fix some general rules, by
which we may know when they really are so.

(1) The cause and effect must be contiguous in space and time.

(2) The cause must be prior to the effect.

(3) There must be a constant union betwixt the cause and effect. It is
chiefly this quality, that constitutes the relation.

(4) The same cause always produces the same effect, and the same effect
never arises but from the same cause. This principle we derive from
experience, and is the source of most of our philosophical reasonings.
For when by any clear experiment we have discovered the causes or
effects of any phaenomenon, we immediately extend our observatio