In our everyday lives we are familiar with making choices. We choose what to wear and what to have for breakfast. We are also aware of the constraints on our choices. You can't choose to wear a red shirt if you don't have one.
All familiar and obvious stuff. Until the philosophers weigh in...
Suppose, they say, that all our actions can be fully described in cause-and-effect terms by the laws of physics. Wouldn't that mean that the outcome of our choices is inevitable? And therefore that the freedom of our choices is illusory?
The answer is that, no, in a physically determined world, our choices would be neither inevitable nor illusory.
The hidden assumption in the free-will dilemma is that the determination of an outcome on one mode of description (physics) excludes a determination of that outcome on another mode of description (the intentional, which is expressed in our everyday language of purpose and choice). So for the Determinists free will is impossible. For the Free-Willers physical determinism is impossible. However, as I will demonstrate below, the above assumption is false: the physical description does not compete with the intentional description but instead is logically complementary to it. [1]
As an example of complementary modes of description, consider a computer that calculates the sum of two numbers. At one level of description, the answer that the computer gives is fully determined by the rules of arithmetic. At another level of description, the answer is fully determined by physical cause and effect in the computer. Not surprisingly, since the computer has been programmed to follow the rules of arithmetic, the physical and arithmetic descriptions are complementary, not mutually exclusive.
In a similar vein, our choices are free on the intentional mode of description because there cannot exist, even in principle, a physical description of the future state of our brain that we would be logically compelled to accept as correct. While we would be correct to accept a physical description that includes the change in brain state entailed by our acceptance of it, we would also be correct to reject it. Why? Because our rejection of it would result in a physical brain state that differed from the physical description we were originally considering. Therefore we would also be correct in our rejection of it. So both possibilities are always logically open to us. It's not merely that we wouldn't know whether the physical description is correct or not (an epistemological issue). It's that no physical description of our brain state can possibly exist that would be inevitable for us to choose (an ontological issue). So the shared hidden assumption of the Determinists and Free-Willers is false as a matter of logic. [2]
When we employ our everyday language concepts of purpose and choice, we are operating at a different level of abstraction to that of scientists when they describe the physical laws of the universe. The free-will dilemma is dissolved when we realize that it is our familiar everyday contexts that define our choices and constraints, not the mathematical laws of physics (where intentional concepts are inapplicable). The dilemma only arises when the terms that apply to one mode of description are taken out of their context and applied to a different mode of description.
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[1] This view is known as Compatibilism. According to a 2009 survey, the ratio of opinions among philosophers is: compatibilism 59.1%; libertarian free will 13.7%; no free will 12.2%; other 14.9%.
[2] This insight is originally from physicist Donald M MacKay ("What Determines My Choice" in his book "The Open Mind and other essays").
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