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, tho' perhaps we may avoid those expressions. Motion in one body in all past instances, that have fallen under our observation, is follow'd 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 infiuence feels the necessity. As there is the same constancy, and the same influence in what we all 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 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 experience'd union has
