The second relation I shall observe as essential to causes and effects, is not so universally acknowledged, but is liable to some controversy. 'Tis that of _priority_ of time in the cause before the effect. Some pretend that 'tis 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 cotemporary 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. 'Tis 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 possessed. Now if any cause may be perfectly cotemporary with its effect, 'tis certain, according to this maxim, that they must all of them be so; since any one of them, which retards its operation for a single moment, exerts not itself at that very individual time, in which it might have operated; and therefore is no proper cause. The consequence of this would be no less than the destruction of that succession of causes, which we observe in the world; and indeed the utter annihilation of time. For if one cause were cotemporary with its effect, and this effect with _its_ effect, and so on, 'tis plain there would be no such thing as succession, and all objects must be co-existent. If this argument appear satisfactory, 'tis well. If not, I beg the reader to allow me the same liberty, which I have used in the preceding case, of supposing it such. For he shall find, that the affair is of no great importance. Having thus discovered or supposed the two relations of _contiguity_ and _succession_ to be essential to causes and effects, I find I am stopped short, and can proceed no farther in considering any single instance of cause and effect. Motion in one body is regarded upon impulse as the cause of motion in another. When we consider these objects with the utmost attention, we find only that the one body approaches the other; and that the motion of it precedes that of the other, but without any sensible interval. 'Tis in vain to rack ourselves with _farther_ thought and reflection upon this subject. We can go no _farther_ in considering this particular instance. Should any one leave this instance, and pretend to define a cause, by saying it is something productive of another, 'tis evident he would say nothing. For what does he mean by _production_? Can he give any definition of it, that will not be the same with that of causation? If he can, I desire it maybe produced. If he cannot, he here runs in a circle, and gives a synonymous term instead of a definition.