A Treatise of Human Nature · Book II · Part III · Section I (2/2)

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, discovers the impossibility of his escape, as well from the obstinacy of the jailer, 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 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 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.

I dare be positive no one will ever endeavour to refute these reasonings otherwise than by altering my definitions, and assigning a different meaning to the terms of cause, and effect, and necessity, and liberty, and chance. According to my definitions, necessity makes an essential part of causation; and consequently liberty, by removing necessity, removes also causes, and is the very same thing with chance. As chance is commonly thought to imply a contradiction, and is at least directly contrary to experience, there are always the same arguments against liberty or free-will. If anyone alters the definitions, I cannot pretend to argue with him, until I know the meaning he assigns to these terms.