I find in the first place, that whatever objects are considered as causes or effects, are contiguous; and that nothing can operate in a time or place, which is ever so little removed from those of its existence.
Though distant objects may sometimes seem productive of each other, they are commonly found upon examination to be linked by a chain of causes, which are contiguous among themselves, and to the distant objects; and when in any particular instance we cannot discover this connexion, we still presume it to exist.

We may therefore consider the relation of CONTIGUITY as essential to that of causation; at least may suppose it such, according to the general opinion, till we can find a more [Part IV.Sect.

5.] proper occasion to clear up this matter, by examining what objects are or are not susceptible of juxtaposition and conjunction.
The second relation I shall observe as essential to causes and effects, is not so universally acknowledged, but is liable to some controversy.
It is that of PRIORITY Of time in the cause before the effect.

Some pretend that it is not absolutely necessary a cause should precede its effect; but that any object or action, in the very first moment of its existence, may exert its productive quality, and give rise to another object or action, perfectly co-temporary with itself.

But beside that experience in most instances seems to contradict this opinion, we may establish the relation of priority by a kind of inference or reasoning.
It is an established maxim both in natural and moral philosophy, that an object, which exists for any time in its full perfection without producing another, is not its sole cause; but is assisted by some other principle, which pushes it from its state of inactivity, and makes it exert that energy, of which it was secretly possest.