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 observation to every phenomenon of the same kind, without waiting for that constant repetition, from which the first idea of this relation is derived.
(5) There is another principle, which hangs upon this, viz.

that where several different objects produce the same effect, it must be by means of some quality, which we discover to be common amongst them.