Agnosticism is logically incoherent (St. Anselm and Alvin Plantinga)

[Langdell]

This post was inspired by an analysis I just read of St. Anselm’s famous “ontological argument” for the existence of God. The analysis was written by Alvin Plantinga, probably the leading philosopher today who advocates theism in his philosophical work. (Plantinga is a Protestant, but that doesn’t have a bearing on his analysis of Anselm’s ontological argument.)

To cut a long story short … Plantinga reworks Anselm’s proof into the following form:

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal greatness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally great.)
2. If a being is maximally great in one possible world, then he must be maximally great in all possible worlds. (In other words, if he’s not maximally great in all possible worlds, then he can’t be maximally great, because he wouldn’t be as great as a being that is maximally great in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally great (i.e., God) in our world.

As Plantinga acknowledges, this argument won’t convince an atheist, because s/he can simply deny the first premise. But this argument does show, it seems to me, that agnosticism is logically incoherent, if we take “agnosticism” to mean holding the position that there might be a God.

According to Plantinga’s reworking of Anselm, the proposition “there might be a God” doesn’t make sense because God, as a being that is maximally great, must exist if his existence is at all possible. In other words, the only positions respecting the existence of God that are logically coherent are the following:

A. God exists.

B. God does not exist.

C. God does not exist, but god-like beings that are less than maximally great might exist.

D. I’m undecided.

Importantly, position D is not the same as holding “God might exist.” The proposition “God might exist” is equivalent to saying, “There’s an X% chance that God exists.” But chances and odds with respect to maximal greatness (God) don’t make sense, because if the chances were anything other than 0%, then maximal greatness would have to exist. God either exists or is impossible.

.

 

[liquidpele]

First, you don’t define “great”… it’s subjective. Great at math? Great at speed? Great at showing love? Great at destroying ancient cities? Second, the entire premise that something maximally great in one place would be the same in another - it could certainly be relative. As a for-instance, c is the speed of light in a vacuum, but in different substances light travels though it slower. The maximum “greatness” in this case depends on where you’re looking. Third, I’m not sure why so many try to come up with a bullet list of why God exists or doesn’t… isn’t the whole idea supposed to be based on faith?

 

[anEvilAtheist]

In other words, the only positions respecting the existence of God that are logically coherent are the following:

A. God exists.

B. God does not exist.

C. God does not exist, but god-like beings that are less than maximally great might exist.

D. I’m undecided.

Importantly, position D is not the same as holding “God might exist.” The proposition “God might exist” is equivalent to saying, “There’s an X% chance that God exists.” But chances and odds with respect to maximal greatness (God) don’t make sense, because if the chances were anything other than 0%, then maximal greatness would have to exist. God either exists or is impossible.

I think that the traditional definitions of agnosticism would fall under option D. Agnosticism deals with knowledge, and agnostics simply claim that they don’t know whether God exists. They don’t need to think you can put odds on the chance that he exists. Agnostics do not know whether God exists and do not even need to know whether it’s possible that he does. I think that when most people say that something is possible, they mean that it’s possible that it’s possible, i.e. they don’t know enough to be able to be able to rule it out with certainty.

 

[fosio]

This post was inspired by an analysis I just read of St. Anselm’s famous “ontological argument” for the existence of God. The analysis was written by Alvin Plantinga, probably the leading philosopher today who advocates theism in his philosophical work. (Plantinga is a Protestant, but that doesn’t have a bearing on his analysis of Anselm’s ontological argument.)

To cut a long story short … Plantinga reworks Anselm’s proof into the following form:

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal greatness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally great.)
2. If a being is maximally great in one possible world, then he must be maximally great in all possible worlds. (In other words, if he’s not maximally great in all possible worlds, then he can’t be maximally great, because he wouldn’t be as great as a being that is maximally great in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally great (i.e., God) in our world.

As Plantinga acknowledges, this argument won’t convince an atheist, because s/he can simply deny the first premise. But this argument does show, it seems to me, that agnosticism is logically incoherent, if we take “agnosticism” to mean holding the position that there might be a God.

According to Plantinga’s reworking of Anselm, the proposition “there might be a God” doesn’t make sense because God, as a being that is maximally great, must exist if his existence is at all possible. In other words, the only positions respecting the existence of God that are logically coherent are the following:

A. God exists.

B. God does not exist.

C. God does not exist, but god-like beings that are less than maximally great might exist.

D. I’m undecided.

Importantly, position D is not the same as holding “God might exist.” The proposition “God might exist” is equivalent to saying, “There’s an X% chance that God exists.” But chances and odds with respect to maximal greatness (God) don’t make sense, because if the chances were anything other than 0%, then maximal greatness would have to exist. God either exists or is impossible.

.

You are confusing or conflating epistemological possibility with logical or metaphysical possibility. Plantinga’s modal ontological argument deals strictly with the latter. Plantinga himself does not claim his argument has any dialectical value against agnosticism or atheism.

 

[hatsoff]

This post was inspired by an analysis I just read of St. Anselm’s famous “ontological argument” for the existence of God. The analysis was written by Alvin Plantinga, probably the leading philosopher today who advocates theism in his philosophical work. (Plantinga is a Protestant, but that doesn’t have a bearing on his analysis of Anselm’s ontological argument.)

To cut a long story short … Plantinga reworks Anselm’s proof into the following form:

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal greatness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally great.)
2. If a being is maximally great in one possible world, then he must be maximally great in all possible worlds. (In other words, if he’s not maximally great in all possible worlds, then he can’t be maximally great, because he wouldn’t be as great as a being that is maximally great in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally great (i.e., God) in our world.

As Plantinga acknowledges, this argument won’t convince an atheist, because s/he can simply deny the first premise. But this argument does show, it seems to me, that agnosticism is logically incoherent, if we take “agnosticism” to mean holding the position that there might be a God.

According to Plantinga’s reworking of Anselm, the proposition “there might be a God” doesn’t make sense because God, as a being that is maximally great, must exist if his existence is at all possible. In other words, the only positions respecting the existence of God that are logically coherent are the following:

A. God exists.

B. God does not exist.

C. God does not exist, but god-like beings that are less than maximally great might exist.

D. I’m undecided.

Importantly, position D is not the same as holding “God might exist.” The proposition “God might exist” is equivalent to saying, “There’s an X% chance that God exists.” But chances and odds with respect to maximal greatness (God) don’t make sense, because if the chances were anything other than 0%, then maximal greatness would have to exist. God either exists or is impossible.

.

You can’t construct a Kripke model with “God exists” in all possible worlds, and then turn around and claim our world is a possible world in that Kripke model–not without some serious justification, that is.

Laypeople often misunderstand Plantinga’s argument because they’re unfamiliar with possible world semantics. In short, though, you must either give up premise (2) or (3). It’s your choice, but one of them has to go.

 

[tjm190]

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal jolliness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally jolly.)
2. If a being is maximally jolly being in one possible world, then he must be maximally jolly in all possible worlds. (In other words, if he’s not maximally jolly in all possible worlds, then he can’t be maximally jolly, because he wouldn’t be as great as a being that is maximally jolly in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally jolly being (i.e., Santa) in our world.

 

[Langdell]

You are confusing or conflating epistemological possibility with logical or metaphysical possibility. Plantinga’s modal ontological argument deals strictly with the latter. Plantinga himself does not claim his argument has any dialectical value against agnosticism or atheism.

This is interesting to me. Could you please explain it further? Thanks.

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[fosio]

This is interesting to me. Could you please explain it further? Thanks.

.

I don’t think I can explain this further. I would take some philosophy courses or read some philosophy texts. This might be a good place to start

plato.stanford.edu/contents.html

 

[Langdell]

You can’t construct a Kripke model with “God exists” in all possible worlds, and then turn around and claim our world is a possible world in that Kripke model–not without some serious justification, that is.

Laypeople often misunderstand Plantinga’s argument because they’re unfamiliar with possible world semantics. In short, though, you must either give up premise (2) or (3). It’s your choice, but one of them has to go.

Could you explain further how possible world semantics work? I really want to understand Plantinga. Thanks.

EDIT: Never mind – someone else helped me out with it.

.

 

[hatsoff]

Could you explain further how possible world semantics work? I really want to understand Plantinga. Thanks.

I can’t tell you in a forum post, no. It’s a robust logical system with complex axioms and theorems. However, I can give you a starting point…

In Kripke’s possible world semantics, a “possible world” is just a particular kind of “set” (as in a mathematical set) of propositions. Not all sets of propositions are possible worlds, but all possible worlds are sets of propositions.

The real, physical world, is not literally a possible world in Kripke’s modal semantics. Instead, we often assume that one of the possible worlds in a “model” describes our world.

So, what is a model? Well, that can be a bit complicated. However, we should note for the moment that a model includes (but is not limited to) a set of possible worlds. In other words, we have a set of sets of propositions.

Suppose our model includes Q such that

Q = { W1, W2, W3,… }

where W1, W2, W3,… are possible worlds.

Then W1 = { P1-1, P1-2, P1-3, … }

where P1-1, P1-2, P1-3,… are propositions.

So this gives us

Q = { { P1-1, P1-2, P1-3, … }, { P2-1, P2-2, P2-3, … }, { P3-1, P3-2, P3-3, … }, … }

Now, each of the propositions are said to be true at their respective worlds. So, for example, P1-1, P1-2, P1-3,… are all true at world W1. They may or may not be true at other worlds.

So, with this in mind, we may now introduce definitions of “possibly” and “necessarily”. A proposition P is possibly true at W and with respect to Q if and only if (hereafter “iff”) W is in Q, and there is a world X in Q with P in X. In other words, P is possibly true iff there is at least one world in our model where P is true.

Meanwhile, P is necessarily true with respect to Q iff for each W in Q we have P in W. In other words, P is necessarily true iff P is true at every single possible world in Q.

Now, if you’re going to construct a Kripke model where the proposition “God exists” is true at every possible world therein, then since we don’t actually know whether or not “God exists” is a true proposition, we can’t say that our world is among the possible worlds in the model.

If, on the other hand, we want to make sure that our world is represented by a possible world in some Kripke model, then we don’t get to say that “God exists” is necessarily true, since, as mentioned before, we don’t know whether or not “God exists” is true in the real world.

I hope that helps.

 

[Langdell]

Thanks – yes, that’s very helpful!

Not to be a noodge, but isn’t Plantinga saying that if we hold that God exists in world X, then we can’t deny that God exists in every world?

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[hatsoff]

Thanks – yes, that’s very helpful!

Not to be a noodge, but isn’t Plantinga saying that if we hold that God exists in world X, then we can’t deny that God exists in every world?

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I’ve only read summaries of Plantinga’s paper, and not the paper itself. It’s from 1975 or something, which is too early for my university account to access. However, that may have been precisely what Plantinga was arguing.

Then again, Plantinga is often very wrong when it comes to theistic arguments. His paper on the evolutionary argument against naturalism, for example, is sickeningly unsound. So it wouldn’t surprise me greatly to learn that he committed some egregious error in his modal ontological argument–for example, it could be that he really did see it as a disproof of agnosticism, when it is no such thing.

 

[severntofall]

This post was inspired by an analysis I just read of St. Anselm’s famous “ontological argument” for the existence of God. The analysis was written by Alvin Plantinga, probably the leading philosopher today who advocates theism in his philosophical work. (Plantinga is a Protestant, but that doesn’t have a bearing on his analysis of Anselm’s ontological argument.)

To cut a long story short … Plantinga reworks Anselm’s proof into the following form:

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal greatness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally great.)
2. If a being is maximally great in one possible world, then he must be maximally great in all possible worlds. (In other words, if he’s not maximally great in all possible worlds, then he can’t be maximally great, because he wouldn’t be as great as a being that is maximally great in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally great (i.e., God) in our world.

As Plantinga acknowledges, this argument won’t convince an atheist, because s/he can simply deny the first premise. But this argument does show, it seems to me, that agnosticism is logically incoherent, if we take “agnosticism” to mean holding the position that there might be a God.

.

I’ve said it a million times, St Anselm was a moron with way too much time on his hands. There were some very intelligent Catholic theologians in the past, Anselm simply was not one of them.

 

[Langdell]

I’ve only read summaries of Plantinga’s paper, and not the paper itself. It’s from 1975 or something, which is too early for my university account to access. However, that may have been precisely what Plantinga was arguing.

Then again, Plantinga is often very wrong when it comes to theistic arguments. His paper on the evolutionary argument against naturalism, for example, is sickeningly unsound. So it wouldn’t surprise me greatly to learn that he committed some egregious error in his modal ontological argument–for example, it could be that he really did see it as a disproof of agnosticism, when it is no such thing.

I don’t want to make him look bad. In the piece I read (it’s included in The Analytic Theist), he doesn’t make an explicit connection with agnosticism. All he claims is that the argument shows theism not to be irrational (which I take it is his usual claim).

.

 

[warpspeedpetey]

This post was inspired by an analysis I just read of St. Anselm’s famous “ontological argument” for the existence of God. The analysis was written by Alvin Plantinga, probably the leading philosopher today who advocates theism in his philosophical work. (Plantinga is a Protestant, but that doesn’t have a bearing on his analysis of Anselm’s ontological argument.)

To cut a long story short … Plantinga reworks Anselm’s proof into the following form:

1. It is possible to conceive of a state of affairs (or, as Plantinga puts it, a “possible world”) in which maximal greatness is instantiated. (“Instantiated” meaning basically that there is a being that is maximally great.)
2. If a being is maximally great in one possible world, then he must be maximally great in all possible worlds. (In other words, if he’s not maximally great in all possible worlds, then he can’t be maximally great, because he wouldn’t be as great as a being that is maximally great in all possible worlds.)
3. Our world is a possible world. (If it weren’t possible, then it wouldn’t exist.)
4. Therefore, there must be a being that is maximally great (i.e., God) in our world.

As Plantinga acknowledges, this argument won’t convince an atheist, because s/he can simply deny the first premise. But this argument does show, it seems to me, that agnosticism is logically incoherent, if we take “agnosticism” to mean holding the position that there might be a God.

According to Plantinga’s reworking of Anselm, the proposition “there might be a God” doesn’t make sense because God, as a being that is maximally great, must exist if his existence is at all possible. In other words, the only positions respecting the existence of God that are logically coherent are the following:

A. God exists.

B. God does not exist.

C. God does not exist, but god-like beings that are less than maximally great might exist.

D. I’m undecided.

Importantly, position D is not the same as holding “God might exist.” The proposition “God might exist” is equivalent to saying, “There’s an X% chance that God exists.” But chances and odds with respect to maximal greatness (God) don’t make sense, because if the chances were anything other than 0%, then maximal greatness would have to exist. God either exists or is impossible.

.

yeah, i replace “great” with maximal state of being to keep the modality of the arguement consistent. though thats from his modalized argument from contingency. the point being that all the normal qualities that we associate with G-d, omnicscience, omnipotence, omnipresence, are all inferred from this maximals state of being, what Aquinas called actus purus, what plantinga calls great.

 

[warpspeedpetey]

First, you don’t define “great”… it’s subjective. Great at math? Great at speed? Great at showing love? Great at destroying ancient cities? Second, the entire premise that something maximally great in one place would be the same in another - it could certainly be relative. As a for-instance, c is the speed of light in a vacuum, but in different substances light travels though it slower. The maximum “greatness” in this case depends on where you’re looking. Third, I’m not sure why so many try to come up with a bullet list of why God exists or doesn’t… isn’t the whole idea supposed to be based on faith?

modalization uses the whole “possible worlds” idea that descends from leibniz, its not that these possible worlds actually exist but rather that they are possible situations so to speak. there is controversy ion the idea.

Great is just his way of infering actus purus, or i prefer the “maximal state of being”

and belief in G-ds existence as a rational idea is generally based on various Thomistic philosophies, i prefer contingency and first cause.

 

[warpspeedpetey]

You can’t construct a Kripke model with “God exists” in all possible worlds, and then turn around and claim our world is a possible world in that Kripke model–not without some serious justification, that is.

Laypeople often misunderstand Plantinga’s argument because they’re unfamiliar with possible world semantics. In short, though, you must either give up premise (2) or (3). It’s your choice, but one of them has to go.

you aint kidding about the semantics, maybe the OP should post platingas actual arguements.

 

[Langdell]

you aint kidding about the semantics, maybe the OP should post platingas actual arguements.

This is his actual wording when he restates the argument:

• There is a possible world in which maximal greatness is instantiated.
• Necessarily, a being is maximally great only if it has maximal excellence in every world.
• Necessarily, a being has maximal excellence in every world only if it has omniscience, omnipotence, and moral perfection in every world.

I paraphrased it because I thought it needed to be fleshed out in accordance with what he says in the piece leading up to this point. (I also didn’t realize that there are trained philosophers on this forum – where have you guys been hiding? )

 

[MindOverMatter]

The real, physical world, is not literally a possible world in Kripke’s modal semantics. Instead, we often assume that one of the possible worlds in a “model” describes our world…

Why is it not a possible world?

So, what is a model? Well, that can be a bit complicated. However, we should note for the moment that a model includes (but is not limited to) a set of possible worlds.

In other words, we have a set of sets of propositions.

Suppose our model includes Q such that

Q = { W1, W2, W3,… }

where W1, W2, W3,… are possible worlds.

Then W1 = { P1-1, P1-2, P1-3, … }

where P1-1, P1-2, P1-3,… are propositions.

So this gives us

Q = { { P1-1, P1-2, P1-3, … }, { P2-1, P2-2, P2-3, … }, { P3-1, P3-2, P3-3, … }, … }

Now, each of the propositions are said to be true at their respective worlds. So, for example, P1-1, P1-2, P1-3,… are all true at world W1. They may or may not be true at other worlds.

So, with this in mind, we may now introduce definitions of “possibly” and “necessarily”. A proposition P is possibly true at W and with respect to Q if and only if (hereafter “iff”) W is in Q, and there is a world X in Q with P in X. In other words, P is possibly true iff there is at least one world in our model where P is true…

What stops God from being true in all possible worlds?

Now, if you’re going to construct a Kripke model where the proposition “God exists” is true at every possible world therein, then since we don’t actually know whether or not “God exists” is a true proposition, we can’t say that our world is among the possible worlds in the model…

With out using symbols, accept for those that are most common such as ordinary English, please explain why Gods necessary existence is dependent on our knowledge. Why isn’t it sufficient to say that God is possible?

 

[hatsoff]

Why is it not a possible world?

It’s not defined as such in Kripke semantics.

What stops God from being true in all possible worlds?

Nothing. You can define your Kripke model any way you like. But your definition isn’t necessarily going to line up with reality. You can’t simply define God into existence!

With out using symbols, accept for those that are most common such as ordinary English, please explain why Gods necessary existence is dependent on our knowledge. Why isn’t it sufficient to say that God is possible?

The modal logic definitions of “possible” and “necessary” bear little resemblance to the natural English language definitions of those same words.

If you’re speaking informally, in natural English, then God is certainly possible. And you could even say that in some sense God might be necessary if he exists. But we don’t get to equivocate between “possible” and “necessary” in informal English and formal Kripke semantics, which is what you would need to do in order to make the inference that since God is possibly necessary, therefore God exists.

This topic can be a little confusing, I know. I hope I have made it clear for you.