T 2.3.1.17

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 deriv'd from the same principles. A prisoner, who has neither money nor interest, discovers the impossibility of his escape, as well from the obstinacy of the goaler, as from the walls and bars with which he is surrounded; and in all attempts for his freedom chuses 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 ax 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 pleas'd to call a physical necessity. The same experienc'd 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.