Free will is being able to choose between different actions. If we judge an action (for example, as good or bad) it only makes sense if the action is freely chosen.
Things like advice, persuasion, and prohibition, are pointless unless people have free will. Free will means people can do different things. Different results come from different courses of action. Traditionally, only actions that are freely willed deserve credit or blame. If there is no free will, there is no sense or justice in rewarding or punishing anybody for any action.
There is more than one kind of determinism, but essentially it is the idea that events in the past fully decide (cause) events in the future. It is the same as saying "the universe is like a clockwork instrument". If you knew everything about it, you could predict exactly what will happen. To illustrate this Pierre-Simon Laplace proposed a thought experiment in 1814, which he called Laplace's demon. If determinism is the case, then there can be no free will.
The view that a deterministic universe means people do not have free will is called "incompatibilism". It means if determinism is true, it is incompatible with free will, and so free will does not exist.
Many thinkers do not like what follows from hard determinism, and ideas have been put forwards as to why we do have free will. Here we give just one of these ideas.
Soft determinism (or "compatibilism") tries keep determinism, but still claims that free will is possible. David Hume had this position. According to Hume, free will is not the ability to make a different decision under the same circumstances. Because there may be slight differences in the circumstances, a different decision can be reached. Chrysippos. a stoic philosopher gives the example of a dog which is tied to a cart. This dog can freely decide to follow the cart. William James coined the term "soft determinism" in The dilemma of determinism in 1884. There, James writes "A common opinion prevails that the juice has ages ago been pressed out of the free-will controversy". James went on to argue, just as did Plutarch, that events fall into two groups: the causally determined and the rest.
"I myself believe that all the magnificent achievements of mathematical and physical science – our doctrines of evolution, of uniformity of law, and the rest – proceed from our indomitable desire to cast the world into a more rational shape in our minds than the shape into which it is thrown there by the crude order of our experience. The world has shown itself, to a great extent, plastic to this demand of ours for rationality. How much further it will show itself plastic no one can say...If a certain formula for expressing the nature of the world violates my moral demand, I shall feel as free to to throw it overboard, or at least to doubt it, as if it disappointed my demand of uniformity of sequence...The principle of causality, for example, – what is it but a postulate, an empty name covering a demand that the sequence of events...manifest a deeper kind of belonging of one thing with another than the mere arbitrary juxtaposition which now phenomenally appears?"— William James, The Will to Believe, p. 147
The law assumes we have free will. The job of courts is to find out when people do things and what they were thinking when they decided to do it. For example, think of someone who kills someone else. A court tries to figure out (1) if he or she actually killed the other person, and (2) if he or she decided to do it. The courts do not ask the philosophical question above.
In the past, people such as Democritus saw the universe as deterministic. Some people thought that getting enough information would allow them to predict perfectly what will happen in the future. Modern science, however, is a mixture of deterministic and stochastic theories.
- Aristotle, On Interpretation c. 9 18b 30, Thomas Aquinas, Summa Theologica Part 1, Q.83 a1
- Dijksterhuis E.J. The mechanization of the world picture. Oxford University Press. Introduction: "[nothing] has had a more profound and far-reaching effect than the... conception of the world usually called mechanical or mechanistic".
- An address to Harvard Divinity School students in Divinity Hall on March 13, 1884: William James (1886). "The dilemma of determinism". The Will to Believe: And Other Essays in Popular Philosophy (Reprint ed.). Longmans, Green, and Company. pp. 145 ff. On-line text here
- Boniolo G. and Vidali P. 1999. Filosofia della Scienza, Milan: Mondadori. ISBN 88-424-9359-7
- Bunge, Mario 1967. Scientific research I: the search for system. Berlin: Springer-Verlag. p291 et seq 5.9 Philosophical hypotheses in science. Reprinted 1998 as Philosophy of science. 2 vols, New Brunswick NJ: Transaction.