of Nero; and remembering many other concurrent testimonies we conclude, that those facts were once really existant, and that so many men, without any interest, would never conspire to deceive us; especially since they must, in the attempt, expose themselves to the derision of all their contemporaries, when these facts were asserted to be recent and universally known.  The same kind of reasoning runs through politics, war, commerce, economy, and indeed mixes itself so entirely in human life, that it is impossible to act or subsist a moment without having recourse to it.  A prince, who imposes a tax upon his subjects, expects their compliance.  A general, who conducts an army, makes account of a certain degree of courage.  A merchant looks for fidelity and skill in his factor or super-cargo.  A man, who gives orders for his dinner, doubts not of the obedience of his servants.  In short, as nothing more nearly interests us than our own actions and those of others, the greatest part of our reasonings is employed in judgments concerning them.  Now I assert, that whoever reasons after this manner, does ipso facto believe the actions of the will to arise from necessity, and that he knows not what he means, when he denies it.

All those objects, of which we call the one cause and the other effect, considered in themselves, are as distinct and separate from each other, as any two things in nature, nor can we ever, by the most accurate survey of them, infer the existence of the one from that of the other.  It is only from experience and the observation of their constant union, that we are able to form this inference; and even after all, the inference is nothing but the effects of custom on the imagination.  We must not here be content with saying, that the idea of cause and effect arises from objects constantly united; but must affirm, that it is the very same with the idea of those objects, and that the necessary connexion is not discovered by a conclusion of the understanding, but is merely a perception of the mind.  Wherever, therefore, we observe the same union, and wherever the union operates in the same manner upon the belief and opinion, we have the idea of causes and necessity, though perhaps we may avoid those expressions.  Motion in one body in all past instances, that have fallen under our observation, is followed upon impulse by motion in another.  It is impossible for the mind to penetrate farther.  From this constant union it forms the idea of cause and effect, and by its influence feels the necessity.  As there is the same constancy, and the same influence in what we call moral evidence, I ask no more.  What remains can only be a dispute of words.