Laplace, in his A Philosophical Essay on Probabilities (1825), and d’Holbach, in his The System of Nature (1770), both defend the idea that the truth of determinism shows that free will is an illusion.
Laplace gives a clear statement of the idea behind determinism when he writes,
“All events, even those which on account of their insignificance do not seem to follow the great laws of nature, are a result of it just as necessarily as the revolutions of the sun. In ignorance of the ties which unite such events to the entire system of the universe, they have been made to depend upon final causes or upon hazard ...but these imaginary causes have gradually receded with the widening bounds of knowledge and disappear entirely before sound philosophy, which sees in them only the expression of our ignorance of the true causes.
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We ought then to regard the present state of the universe as the effect of its anterior state and as the cause of the one which is to follow. Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective situation of the beings who compose it -- an intelligence sufficiently vast to submit these data to analysis -- it would embrace in the same formula the movements of the greatest bodies of the universe and those of the lightest atom; for it, nothing would be uncertain and the future, as the past, would be present to its eyes.”
Laplace is suggesting that every future state of the universe is determined by its present state plus the laws of nature. He illustrates this by imagining an intelligence which knows everything about the present state of the universe (‘the respective situation of the beings who compose it’) and the laws of nature (‘all the forces by which nature is animated’). He suggests that, for such an intelligence, the future would appear to have the same kind of necessity as the past seems to us to have. The fact that the future to us seems more open than the past is due to only one thing: our ignorance.
Earlier we discussed fatalism, the view that the future is already fixed. We distinguished between theological arguments for fatalism on the basis of divine foreknowledge and logical arguments for fatalism on the basis of the claim that in the past every proposition about the future or its negation must already have been true. Laplace here is defending a fatalist view, but one whose motivations are distinct from either of the other two forms of fatalism we have discussed. We could call Laplace’s view a causal or scientific fatalism.
d’Holbach explicitly applies this determinist picture of the universe to human beings:
“Man’s life is a line that nature commands him to describe upon the surface of the earth, without his ever being able to swerve from it, even for an instant. He is born without his own consent; his organization does nowise depend upon himself; his ideas come to him involuntarily; his habits are in the power of those who cause him to contract them; he is unceasingly modified by causes, whether visible or concealed, over which he has no control, which necessarily regulate his mode of existence, give the hue to his way of thinking, and determine his manner of acting. ...Nevertheless, in despite of the shackles by which he is bound, it is pretended he is a free agent, or that independent of the causes by which he is moved, he determines his own will, and regulates his own condition.”
What of the fact that it seems to us that we are free? That, when confronted with a choice, it seems to us entirely up to us what we will do? d’Holbach dismisses this as an illusion:
“In despite of these proofs of the want of free agency in man, so clear to unprejudiced minds, it will, perhaps, be insisted upon with no small feeling of triumph, that if it be proposed to any one, to move or not move his hand ...he evidently appears to be the master of choosing; from which it is concluded that evidence has been offered of his free agency. This reply is, this example is perfectly simple; man in performing some action which he is resolved on doing, does not by any means prove his free agency: the very desire of displaying this quality, excited by the dispute, becomes a necessary motive, which decides his will either for the one or the other of these actions ...”
Is this a convincing explanation of our feeling that we have free will?
Both Laplace and d’Holbach seem to think that free will is incompatible with the deterministic nature in which they believed. But Laplace goes one step further, and presents a short argument for the conclusion that, even if some events turn out not to be determined by the prior state of the universe, that these also cannot be free:
“Present events are connected with preceding ones by a tie based on the evident principle that a thing cannot occur without a cause that produces it. This axiom, known by the name of the principle of sufficient reason, extends even to actions which are considered indifferent; the freest will is unable without a determinative motive to give them birth; if we assume two positions with exactly similar circumstances and find that the will is active in the one and inactive in the other, we say that its choice is an effect without a cause. It is then, says Leibnitz, the blind chance of the Epicureans. Th contrary opinion is an illusion of the mind, which, losing sight of the evasive reasons of the choice of the will in indifferent things, believes that choice is determined of itself and without motives.”
The moral of the story we get from Laplace and d’Holbach, then, is this: the universe is deterministic, so that given its state at one time and the laws of nature, every future state of the universe follows of necessity. We are part of the universe, so every future action of ours is similarly determined. Free will is therefore an illusion, as all of our acts are determined by preceding states of the universe, over which we have no control. And even if there should be an exception to determinism, the only intelligible alternative to a determined event is one which occurs purely by chance. And chance is no more amenable to free will than is determinism.