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The argument from free will (AFFW) contends that omniscience and free will are incompatible, and that any conception of God that incorporates both properties is therefore inherently contradictory.
Moses Maimonides formulated an argument, in the traditional manner, in terms of good and evil actions, as follows:
|“||… "Does God know or does He not know that a certain individual will be good or bad? If thou sayest 'He knows', then it necessarily follows that [that] man is compelled to act as God knew beforehand he would act, otherwise God's knowledge would be imperfect.…"||”|
In modern terms, the argument is formulated typically as follows:
- God is defined as a personal being who knows everything. Personal beings have free will.
- In order to have free will, you must have more than one option, each of which is avoidable. This means that before you make a choice, there must be a state of uncertainty during a period of potential: you cannot know the future. Even if you think you can predict your decision, if you claim to have free will, you must admit the potential (if not the desire) to change your mind before the decision is final.
- A being who knows everything can have no "state of uncertainty". It knows its choices in advance.
- A being that knows its choices in advance has no potential to avoid its choices, and therefore lacks free will.
- Since a being that lacks free will is not a personal being, a personal being who knows everything cannot exist.
- Therefore, God does not exist.
The principal criticisms of this argument center around points 1 and 2, though there is some concern regarding point 4. All point numbers refer to Barker's formulation.
Criticism of point 1
- "knows everything that God chooses to know and that is logically possible to know"; Or instead the slightly stronger:
- "knows everything that is logically possible to know"
If omniscient is used in the first sense then the argument's applicability depends on what the god in question chooses to know, and therefore it is not a complete argument against the existence of God. In both cases the argument depends on the assumption that it is logically possible for God to know every choice that he will make in advance of making that choice.
Criticism of point 2
The compatibilist school of thought holds that free will is compatible with determinism and fatalism and therefore does not accept the assumptions of point 2. A related line of thought, which goes back at least to Boethius, holds that God observing someone making a choice does not constrain their choice, although this is in the context of human free will The controversy about this was so well-known in Chaucer's day that he has a somewhat satirical digression on it in The Nun's Priest's Tale.
Criticism of point 4
One criticism of the Argument from Free Will is that in point 4 of the proof it simply assumes that foreknowledge and free will are incompatible. It uses circular logic to "prove" this, by simply stating that "a being that knows its choices in advance has no potential to avoid its choices". Point 4 is therefore saying, in essence, "A being that knows its choices in advance has no free will, and therefore has no free will". By assuming what it is trying to prove, that point undermines the entire argument.
Specifically, point 4 commits the modal fallacy of assuming that because some choice is known to be true, it must be necessarily true (i.e. there is no way it could possibly be false). Logically, the truth value of some proposition cannot be used to infer that the same proposition is necessarily true.
Using logical terminology and applying it to AFFW, there is a marked distinction between the statement "It is impossible (for God to know a future action to be true and for that action to not occur)" and the statement "If God knows that a future action is true, then it is impossible for that action to not occur." While the two statements may seem to say the same thing, they are not logically equivalent. The second sentence is false because it commits the modal fallacy of saying that a certain action is impossible, instead of saying that the two propositions (God knows a future action to be true, and that action does not occur) are jointly impossible. Simply asserting that God knows a future action still leaves the possibility for the action not to occur (i.e. if God is wrong, it might not occur). The confusion comes in mistaking a semantic relation between two events for a causal relation between two events.
With these assumptions more explicitly stated, the proof becomes:
- Assume that person X has free will (assumption).
- By the definition of free will, at any point in time, X can choose to do any action A, where A belongs to A(T), the set of all actions that X is physically capable of at time T (definition of free will).
- At time T, person X will choose to do action A (i.e. a person cannot logically choose to do both A and not A) (Law of the Excluded Middle).
- Assume that an omniscient God exists (assumption).
- By the definition of omniscience, God knows everything that will happen at any point in time (definition of omniscience).
- From 3. and 5., God knows that at time T, person X will choose to do action A (logical conclusion).
- Therefore, person X must do action A at time T.
This claims to prove that at time T, person X is unable to do any action other than A. However, you could also remove steps 4–6, and arrive at the same conclusion. This is called logical determinism, and it suffers from the same modal fallacy as AFFW. If a certain proposition is true, that does not imply that the proposition is logically necessary. Once you remove the invalid assertion, then the argument for logical determinism is shown to be false. Similarly, when that same invalid assertion is removed from AFFW ("by the definitions of 'knowledge' and 'choice', if one knows for certain what choice one will make in the future, one will not be able to make the opposite choice"), the proof is shown to be false.
God is outside of time
C. S. Lewis argues in the book Mere Christianity that God is outside of time and therefore does not "foresee" events, but simply observe them.
|“||But suppose God is outside and above the Time-line. In that case, what we call "tomorrow" is visible to Him in just the same way as what we call today." All the days are "Now" for Him. He does not remember you doing things yesterday, He simply sees you doing them: because, though you have lost yesterday, He has not. He does not "foresee" you doing things tomorrow, He simply sees you doing them: because, though tomorrow is not yet there for you, it is for Him. You never supposed that your actions at this moment were any less free because God knows what you are doing. Well, He knows your tomorrow's actions in just the same way--because He is already in tomorrow and can simply watch you. In a sense, He does not know your action till you have done it: but then the moment at which you have done it is already "Now" for Him.||”|
- See the various controversies on God's Omniscience, and in particular on the critical notion of Foreknowledge
- Stanford Encyclopedia of Philosophy, Foreknowledge and Free Will
- Internet Encyclopedia of Philosophy, Foreknowledge and Free Will
- Though Moses Maimonides was not arguing against the existence of God, but rather for the incompatibility between the full exercise by God of his omniscience and genuine human free will, his argument is considered by some as affected by Modal Fallacy. See, in particular, the article by Prof. Norman Swartz for Internet Encyclopedia of Philosophy, Foreknowledge and Free Will and specifically Section 6: The Modal Fallacy
- The Eight Chapters of Maimonides on Ethics (Semonah Perakhim), edited, annotated, and translated with an Introduction by Joseph I. Gorfinkle, pp. 99–100. (New York: AMS Press), 1966.
- The Freewill Argument for the Nonexistence of God by Dan Barker Freethought Today, August 1997 
- see eg Richard Swinburne Does God Exist? of The Catechism of the Catholic Church
- see eg John Polkinghorne
- see eg the Stanford Encycolpedia of Philosophy article cited above for details of the Boethian view
- Nun's Priest's Tale Lines 3234–3251
- Prof. Norman Swartz, The Modal Fallacy
- Internet Encyclopedia of Philosophy, Foreknowledge and Free Will: The Modal Fallacy
- C. S. Lewis Mere Christianity Touchstone:New York, 1980 p.149
- Free Will - Freethoughtpedia.com original article on the nature of Free Will and how it applies to religion
- The Paradox of Free will - An online discussion