The skin, pores, muscles, and nerves of a day-labourer, are different from those of a man of quality: so are his sentiments, actions, and manners. The different stations of life influence the whole fabric, external and internal; and these different stations arise necessarily, because uniformly, from the necessary and uniform principles of human nature. Men cannot live without society, and cannot be associated without government. Government makes a distinction of property, and establishes the different ranks of men. This produces industry, traffic, manufactures, lawsuits, war, leagues, alliances, voyages, travels, cities, fleets, ports, and all those other actions and objects which cause such a diversity, and at the same time maintain such an uniformity in human life.
Should a traveller, returning from a far country, tell us, that he had seen a climate in the fiftieth degree of northern latitude, where all the fruits ripen and come to perfection in the winter, and decay in the summer, after the same manner as in England they are produced and decay in the contrary seasons, he would find few so credulous as to believe him. I am apt to think a traveller would meet with as little credit, who should inform us of people exactly of the same character with those in Plato's republic on the one hand, or those in Hobbes's Leviathan on the other. There is a general course of nature in human actions, as well as in the operations of the sun and the climate. There are also characters peculiar to different nations and particular persons, as well as common to mankind. The knowledge of these characters is founded on the observation of an uniformity in the actions that flow from them; and this uniformity forms the very essence of necessity.
I can imagine only one way of eluding this argument, which is by denying that uniformity of human actions, on which it is founded. As long as actions have a constant union and connexion with the situation and temper of the agent, however we may in words refuse to acknowledge the necessity, we really allow the thing. Now, some may perhaps find a pretext to deny this regular union and connexion. For what is more capricious than human actions? What more inconstant than the desires of man? And what creature departs more widely, not only from right reason, but from his own character and disposition? An hour, a moment is sufficient to make him change from one extreme to another, and overturn what cost the greatest pain and labour to establish. Necessity is regular and certain. Human conduct is irregular and uncertain. The one therefore proceeds not from the other.
To this I reply, that in judging of the actions of men we must proceed upon the same maxims, as when we reason concerning external objects. When any phenomena are constantly and invariably conjoined together, they acquire such a connexion in the imagination, that it passes from one to the other without any doubt or hesitation. But below this there are many inferior degrees of evidence and probability, nor does one single contrariety of experiment entirely destroy all our reasoning. The mind balances the contrary experiments, and, deducting the inferior from the superior, proceeds with that degree of assurance or evidence, which remains. Even when these contrary experiments are entirely equal, we remove not the notion of causes and necessity; but, supposing that the usual contrariety proceeds from the operation of contrary and concealed causes, we conclude, that the chance or indifference lies only in our judgment on account of our imperfect knowledge, not in the things themselves, which are in every case equally necessary, though, to appearance, not equally constant or certain. No union can be more constant and certain than that of some actions with some motives and characters; and if, in other cases, the union is uncertain, 'tis no more than what happens in the operations of body; nor can we conclude any thing from the one irregularity which will not follow equally from the other.
'Tis commonly allowed that madmen have no liberty. But, were we to judge by their actions, these have less regularity and constancy than the actions of wise men, and consequently are farther removed from necessity. Our way of thinking in this particular is, therefore, absolutely inconsistent; but is a natural consequence of these confused ideas and undefined terms, which we so commonly make use of in our reasonings, especially on the present subject.
We must now show, that, as the union betwixt motives and actions has the same constancy as that in any natural operations, so its influence on the understanding is also the same, in determining us to infer the existence of one from that of another. If this shall appear, there is no known circumstance that enters into the connexion and production of the actions of matter that is not to be found in all the operations of the mind; and consequently we cannot, without a manifest absurdity, attribute necessity to the one, and refuse it to the other.
There is no philosopher, whose judgment is so rivetted to this fantastical system of liberty, as not to acknowledge the force of moral evidence, and both in speculation and practice proceed upon it as upon a reasonable foundation. Now, moral evidence is nothing but a conclusion concerning the actions of men, derived from the consideration of their motives, temper, and situation. Thus, when we see certain characters or figures described upon paper, we infer that the person who produced them would affirm such facts, the death of Cæsar, the success of Augustus, the cruelty of Nero; and, remembering many other concurrent testimonies, we conclude that those facts were once really existent, 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 'tis 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 supercargo. 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. 'Tis 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 'tis the very same with the idea of these 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. 'Tis 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.
And indeed, when we consider how aptly natural and moral evidence cement together, and form only one chain of argument betwixt them, we shall make no scruple to allow, that they are of the same nature, and derived from the same principles. A prisoner, who has neither money nor interest, discover the impossibility of his escape, as well from the obstinacy of the gaoler, as from the walls and bars with which he is surrounded; and in all attempts for his freedom, chooses rather to work upon the stone and iron of the one, than upon the inflexible nature of the other. The same prisoner, when conducted to the scaffold, foresees his death as certainly from the constancy and fidelity of his guards, as from the operation of the axe or wheel. His mind runs along a certain train of ideas: the refusal of the soldiers to consent to his escape; the action of the executioner; the separation of the head and body, bleeding, convulsive motions, and death. Here is a connected chain of natural causes and voluntary actions; but the mind feels no difference betwixt them in passing from one link to another; nor is less certain of the future event than if it were connected with the present impressions of the memory and senses by a train of causes cemented together by what we are pleased to call a physical necessity. The same experienced union has the same effect on the mind, whether the united objects be motives, volitions and actions, or figure and motion. We may change the names of things, but their nature and their operation on the understanding never change.