Tuesday, February 05, 2019

Plantinga's ontological argument for the rationality of theism

I think Alvin Plantinga's ontological argument is often misunderstood both by atheists and by Christian apologists. Alvin Plantinga was not trying to argue that God exists. Rather, he was trying to argue that belief in God is not irrational or unreasonable. He said in his book, God, Freedom, and Evil, "What I claim for this argument, therefore, is that it establishes, not the truth of theism, but its rational acceptability" (page 112).

Lemme explain how I think his argument does that. This is his argument (put in my own words, not his).

1. There is a possible world in which maximal greatness is instantiated.
2. Maximal greatness consists in having omniscience, omnipotence, and moral perfection in all possible worlds.
3. Therefore, a being with omniscience, omnipotence, and moral perfection exists in all possible worlds.
4. If something exists in all possible worlds, then it also exists in the actual world.
5. A being with omniscience, omnipotence, and moral perfection exists in all possible worlds. (from 3)
6. Therefore, a being with omniscience, omnipotence, and moral perfection exists in the actual world.
The whole argument hinges on that first premise. None of the other premises are controversial. So what reason is there to think the first premise is true? One reason (the reason almost always cited) is because there is no obvious contradiction in the notion of maximal greatness. If it isn't logically contradictory, then it's logically possible, so there is a logically possible world in which maximal greatness is instantiated.

But what if we begin with a different premise: There is a possible world in which maximal greatness is *not* instantiated. This premise doesn't seem anymore contradictory than the other premise. Yet it leads to the opposite conclusion. I'm going to shorten the argument a little to get rid of some extra verbiage so should be obvious enough to go without saying.

7. There is a possible world in which maximal greatness is not instantiated.
8. Maximal greatness consists in having omniscience, omnipotence, and moral perfection in all possible worlds
9. Therefore, there isn't a being with maximal greatness in any possible world.
10. Therefore, there isn't a being with maximal greatness in the actual world.
That isn't to say there isn't a being with omnipotence, omniscience, and moral perfection in the actual world, just that if such a being existed, it wouldn't be a necessary being.

So either a maximally great being necessarily exists, or it is impossible. There's no middle ground. And either there is a possible world in which maximal greatness is instantiated or else there is a possible world in which maximal greatness is not instantiated. It's logically impossible for both premises to be true since they each lead necessarily to conclusions that contradict each other.

You can't rule out one of these premises in order to affirm the other because that's circular reasoning. I've talked to both atheists and theists who have tried to do that, and I couldn't get them to see that their reasoning was circular. If there is no non-question-begging way to adjudicate between these two premises, then as far as we know, one is just as likely to be true as the other. With that being the case, then one is not being irrational to affirm either premise. And since the conclusions follow necessarily from the premises, it follows that one is not being irrational in affirming or denying the existence of a maximally great being.

And that means theism is not irrational. It's a modest claim, for sure, but since there are people who think theism is irrational, it's a claim that's worth making.

I wrote more about Plantinga's argument elsewhere. I went into more detail about possible world semantics, so if you had a hard time following the argument in this post, read this one.

2 Comments:

At 2/06/2019 10:05 AM , Blogger Staircaseghost said...

"The whole argument hinges on that first premise. None of the other premises are controversial."

This is incorrect, inasmuch as the second premise is inarguably wrong.

The second premise instantiates maximum wrongness. It possesses wrongness to the highest possible degree. You could spend a lifetime reading philosophy and not stumble across a more wrong statement. It somehow surpasses even the wrongness of the idea that an individual gene could code for a propositional belief, which is also one of Plantinga's, so that's saying something. The wrongness is so great finite minds dare not apprehend it directly, lest they be blasted to ash from the awesome power of its error.

(Logical) modal claims are predications of the ensemble of logically possible worlds. It is a category error to predicate them of individual entities in individual worlds.

I had white wine with dinner last night, but it was logically possible that I could have had red. But having had red wine last night is not a property that I have; it is FALSE to predicate red-wine-having of me.

"There exists a logically possible world where I had red" is a statement that quantifies over the ensemble of LPWs, not one that quantifies over individuals in the actual world.

And all this just in an effort to "prove" that vague deism is, if not quite rational, not not rational!

 
At 2/08/2019 12:08 AM , Anonymous Anonymous said...

There are obviously good arguments for the frst premise.

Great-making property = A property that ultimately entails no limitation or restriction in its possessor.

Lesser-making property = A property that ultimately entails a limitation or restriction in its possessor.


1) If a property is a great-making property, then its negation is a lesser-making property

2) Great-making properties cannot entail lesser-making properties

3) Maximal greatness is a great-making property

C: Maximal greatness is possible

The first premise is clearly true since a great-making property is one that entails no limitations. Its negation, are properties that entail limitations in its possessors, namely lesser-making properties.

The second premise is also true since lesser-making properties entail limitations. If the great-making properties can entail lesser-making properties, then they would in this case entail limitations. But great-making properties, by definition, do not entail limitations. So great-making properties can not entail lesser-making properties.

Maximal greatness is the quality of having the largest array of the great-making properties. Since that would only include great-making properties and great-making properties by definition do not entail limitations then maximal greatness does not entail limitations (great-making property).

From 2 and 3, it follows that a being that has maximal greatness can not contain any lesser-making properties. From that conclusion and premise 1, it follows that the being that has maximal greatness does not have any negations of great-making properties. Since the being with all the great-making properties (maximally great being) does not have any property and its negation, there are no contradictions making it a possible being.

 

Post a Comment

Subscribe to Post Comments [Atom]

<< Home