But, whilst none have scrupled to admit necessity as influencing matter, many have disputed its dominion over mind. Independently of its militating with the received ideas of the justice of God, it is by no means obvious to a superficial inquiry. When the mind observes its own operations, it feels no connection of motive and action: but as we know ’nothing more of causation than the constant conjunction of objects and the consequent inference of one from the other, as we find that these two circumstances are universally allowed to have place in voluntary action, we may be easily led to own that they are subjected to the necessity common to all causes.’ The actions of the will have a regular conjunction with circumstances and characters; motive is to voluntary action what cause is to effect. But the only idea we can form of causation is a constant conjunction of similar objects, and the consequent inference of one from the other: wherever this is the case necessity is clearly established.
The idea of liberty, applied metaphorically to the will, has sprung from a misconception of the meaning of the word power. What is power?—id quod potest, that which can produce any given effect. To deny power is to say that nothing can or has the power to be or act. In the only true sense of the word power, it applies with equal force to the lodestone as to the human will. Do you think these motives, which I shall present, are powerful enough to rouse him? is a question just as common as, Do you think this lever has the power of raising this weight? The advocates of free-will assert that the will has the power of refusing to be determined by the strongest motive; but the strongest motive is that which, overcoming all others, ultimately prevails; this assertion therefore amounts to a denial of the will being ultimately determined by that motive which does determine it, which is absurd. But it is equally certain that a man cannot resist the strongest motive as that he cannot overcome a physical impossibility.