Voltaire was the pen name of François-Marie Arouet. In his Enlightenment masterpiece Dictionnaire Philosophique, his entry on Franc arbitre was largely his reading of John Locke, especially the section On Power from Locke's Essay on Human Understanding. Voltaire reads Locke as saying our actions are completely caused and freedom is merely freedom of action. He concludes that man is a machine governed by eternal laws. If not, we would be subject to pure caprice. This combination is the standard argument against free will.
Free Will, from the Philosophical Dictionary
From the commencement of the time in which men began to reason, philosophers have agitated this question, which theologians have rendered unintelligible by their absurd subtleties upon grace. power of action. The words liberty and free-will are, then, abstractions, general terms, like beauty, goodness, justice. These terms do not signify that all men are always handsome, good, and just, neither are they always free. Further, liberty being only the power of acting, — what is this power? It is the effect of the constitution, and the actual state of our organs. Leibnitz would solve a problem of geometry, but falls into an apoplexy: he certainly has not the liberty to solve his problem. A vigorous young man, passionately in love, who holds his willing mistress in his arms, is he free to subdue his passion? doubtless not. He has the power of enjoying, and has not the power to abstain. Locke is then very right in calling liberty, power. When can this young man abstain, notwithstanding the violence of his passion? when a stronger idea shall determine the springs of his soul and body to the contrary. But how? have other animals the same liberty, the same power? Why not? They have sense, memory, sentiment, and perceptions like ourselves; they act spontaneously as we do. They must also, like us, have the power of acting by virtue of their perception, and of the play of their organs. We exclaim, — if it be thus, all things are machines merely; everything in the universe is subjected to eternal laws. Well, would you have everything rendered subject to a million of blind caprices? Either all is the consequence of the nature of things, or, all is the effect of the eternal order of an absolute master; in both cases we are only wheels to the machine of the world.Locke is perhaps the first, who, without having the arrogance of announcing a general principle, has examined human nature by analysis. It has been disputed for three thousand years, whether the will is free or not; Locke shows, that the question is absurd, and that liberty cannot belong to the will any more than colour and motion. What is meant by the expression to be free? It signifies power, or rather it has no sense at all. To say that the will can, is in itself as ridiculous as if we said that it is yellow, or blue, round or square. Will is will, and liberty is power. Let us gradually examine the chain of what passes within us, without confusing our minds with any scholastic terms, or antecedent principle. It is proposed to you to ride on horseback, it is absolutely necessary for you to make a choice, for it is very clear that you must either go or not; there is no medium, you must absolutely do the one or the other. So far it is demonstrated that the will is not free. You will get on horseback? why? Because I will to do so, an ignoramus will say. This reply is an absurdity, nothing can be done without reason or cause. Your will then is caused by what? the agreeable idea which is presented to your brain; the predominant, or determinate idea; but, you will say, cannot I resist an idea which predominates over me? No, for what would be the cause of your resistance? an idea by which your will is swayed still more despotically. You receive your ideas, and, therefore, receive your will. You will then necessarily; consequently, the word liberty belongs not to will in any sense. You ask me, how thought and will are formed within you? I answer, that I know nothing about it. I no more know how ideas are created, than I know how the world was formed. We are only allowed to grope in the dark in reference to all that inspires our incomprehensible machine. Will, then, is not a faculty which can be called free. A free-will is a word absolutely void of sense; and that which scholars have called indifference, that is to say, will without cause, is a chimera, unworthy to be combatted. In what then consists liberty? In the power of doing what we will? I would go into my cabinet, the door is open, I am free to enter. But say you, if the door is shut and I remain where I am, I remain freely? Let us explain ourselves; — you then exercise the power that you possess of remaining, you possess this power, but not the power of going out. Liberty, then, on which so many volumes have been written, reduced to its proper sense, is only the power of acting. In what sense must the expression "this man is free" be spoken? In the same sense in which we use the words health, strength, and happiness. Man is not always strong, healthy, or happy. A great passion, a great obstacle, may deprive him of his liberty, or
Franc Arbitre, de la Dictionnaire Philosophique