Saturday, October 20, 2018


(For my MCCC Philosophy of Religion students.)


#1 - To defeat Mackie's argument all Plantinga needs to do is show that there is a possible world in which Mackie's Triad can be affirmed. If Mackie's Triad was logically inconsistent, there could be no possible world where an all-powerful, all-loving being existed with the existence of evil.

Plantinga does this by showing a possible world where:

#2 - It is possible that God has given persons libertarian free will.

"Libertarian free will" is: the ability to make a choice (such as, e.g., a moral choice) that is not fully reducible to antecedent (or prior) causal conditions. For example, making a moral choice not fully reducible to neurochemistry, environmental conditions, or both. 

#3 - It is possible that God has counterfactual knowledge.

To say that God could have counterfactual knowledge is to say that God knows the truth value of future conditional statements that describe possible states of affairs. (Note: if one thinks that God's counterfactual knowledge eliminates free will they have just made an error in modal logic - see 

For example: If John faces a moral choice tonight then either

a) John will choose good; or
b) John will choose evil.

It is possible that God knows which choice John will make. (All that's needed here is logical possibility, not actuality).

If God knows John will choose evil, then God cannot make a world where there is no evil, since to do that would contradict John's having libertarian free will.

But what if, Mackie asks, God made a world where all persons on all occasions chose good? Plantinga responds by saying that it is possible transworld depravity exists. 

#4 - It is possible that transworld depravity exists.

By "transworld depravity" Plantinga means: in all possible worlds human agents will commit at least one evil act.

If, then, there is a possible world where libertarian free will exists and God knows what choices John will make, and knows that John will choose evil on at least one occasion, then God cannot make a world where John is faced with that choice and chooses good. This is because it would violate John's free will.

If so, then we have a world where one can affirm the existence of an all-powerful and all-loving (as well as all-knowing) God exists, as does evil. Mackie's logical argument is defeated.