Alvin Plantinga is widely regarded as one of the world’s leading Christian philosophers. Watch the video below and ask yourself, WTF?
So as not to spoil your fun, I’ll refrain from offering my take on the argument until readers have had a chance to comment.
Plantinga’s argument isn’t about what’s true in various possible worlds, it’s about what’s possibly true in our world.
What’s possibly true in our world IS a matter of what’s true in various possible worlds (unless one is confusing epistemic possibilities with the kind of metaphysical possibilities Plantinga is discussing, and I know a man with your epic modal logic skills would never do that).
Forgive me if I don’t spend any more time studying your “arguments” about how astonishingly lame Plantinga is at modal logic. Ich habe genug.
walto,
Slow down! You’re making silly mistakes.
You wrote:
You’ve got it exactly backwards.
Plantinga’s argument employs epistemic possibility. It’s obvious, if you’d just slow down and think about it.
Plantinga wants to demonstrate a truth about our world — namely, that Alvin is not identical to Alvin’s body. Now, it is already a fact that Alvin either is, or isn’t, identical to his body, whether we know it or not. The other possibility is closed off metaphysically.
Epistemically, however, it is not closed off, because we don’t yet know whether Alvin is identical to his body. Plantinga wants us to conclude that it isn’t possible — in other words, he wants us to close off the epistemic possibility that Alvin is identical to his body, and he wants us to do it on the basis of his argument.
And since we are dealing with epistemic possibilities, your statement is wrong:
walto:
I’d encourage you to take a break and come back when you’re thinking more clearly.
That may be an argument (a bad one), but it’s not Plantinga’s.
You’re free to make a case for your interpretation of Plantinga’s argument. If you do, I’ll look it over and tell you what I think.
I gave my interpretation (i.e., the standard one) back on 4/8. To wit:
Plantinga’s argument is this:
1. If my body were identical to me, then my body and me would have all and only the same properties.
2. But there are some modal properties that my body has that I don’t have and vice versa.
3. Therefore, I am not my body.
That’s his (i.e., the classic) argument. It’s been made at least since Descartes. It requires de re reference as Plantinga well knows, and has nothing to do with epistemic possibilities, from which you couldn’t get even a valid argument, never mind a sound one. At one point, several weeks ago, I thought you were starting to understand this stuff, but I don’t think so anymore. Or if you did, you’ve forgotten.
walto,
Up to that point, your description matches mine, except that I correctly identified the single modal property in question:
Where you really go off the rails is in the next bit, when you write:
He isn’t saying “I can conceive of my body having modal properties that I don’t share; therefore my body actually does have modal properties that I don’t share.” Plantinga isn’t stupid, Walt. Conceiving of something does not guarantee its truth.
He actually identifies a modal property that he thinks is not shared between Alvin and Alvin’s body. It’s the property I mentioned in my version:
He identifies that specific property as belonging to Alvin, but not to Alvin’s body, and concludes via Leibniz’s Law that Alvin is not identical to Alvin’s body.
You’re trying to rebut Plantinga’s argument by saying, “Well, one of the premises might be wrong, so Plantinga’s argument might be wrong.” That’s hardly a refutation!
No wonder you didn’t want to quote that part.
To actually refute the argument, you need to show that it is wrong, not that it merely might be wrong.
As I’ve explained many times, the way to refute it is by showing that Plantinga mistakenly applies Leibniz’s Law to a de dicto reference.
walto,
Of course Plantinga can’t get a sound argument from epistemic possibilities. That’s why his argument is bogus!
“Alvin can possibly exist without Alvin’s body” is an epistemic possibility, and that’s precisely why it is de dicto, not de re. You can’t apply Leibniz’s Law to de dicto properties, so Plantinga’s argument fails.
Geez, Walt.
“Epistemic possibility” doesn’t actually name a modal property at all: it’s a misnomer, as I’ve explained here previously.
Hold that thought, Walt! You’re getting really, really close to actually understanding this.
Yes, an epistemic possibility is not a modal property of its referent. That’s Plantinga’s exact mistake.
Epistemic possibilities are de dicto. Plantinga needs a de re property before he can invoke Leibniz’s Law.
He has mistaken an epistemic possibility, which is de dicto, for an actual modal property, which would be de re.
If I say “I can conceive of cameras having antlers”, I am not describing a modal property of cameras, I am describing a non-modal property of me: can conceive of cameras having antlers.
Likewise, when Plantinga says “I can conceive of Alvin continuing to exist after Alvin’s body has been destroyed”, he isn’t describing a modal property of Alvin, he’s describing a non-modal property of his own mind.
Now, the twist is that Plantinga and Alvin are the same person, so “a non-modal property of his own mind” is really “a non-modal property of Alvin”. Given this fact, you might ask “Isn’t a non-modal property of Alvin good enough for the purposes of the argument?”
The answer is no, because Plantinga needs to find a property of himself that cannot be a property of his body (or vice-versa). He can’t say that the property “Can conceive of himself as existing when his body doesn’t” is a property of both Alvin and Alvin’s body without assuming his conclusion: namely, that Alvin is not identical to Alvin’s body.
In short:
Epistemic possibilities are de dicto.
Modal properties are de re.
Plantinga has mistaken an epistemic possibility for a modal property.
He applies Leibniz’s Law, which requires de re references, to an epistemic possibility, which is de dicto.
Therefore, his argument fails.
I’ve indicated my problems with your rewrite of Plantinga about 30 times now. I suggest you send it to him and let him tell you himself whether he thinks you’ve got him right. I’ll throw in $10 if he does so.
Oh, and thanks so much for grading my modal logic (and other) capacities for me in every post. I can’t tell you how much it means for me to get such a big shot /know-all to assess my work. Heaven knows it’s more than I deserve!
I think the following proof demonstrates the power of Plantinga’s modal argument.
a = b
a squared = ab
a squared – b squared = ab-b squared
(a-b)(a+b) = b(a-b)
a+b = b
b+b = b
2b = b
2 = 1
The modal argument is the linguistic equivalent of dividing by zero.
And, given that, you can also prove that McTaggart is the Pope.
walto,
Yes, and I’ve carefully explained why your objections fail. Is there a particular objection you would like to raise again, taking my criticisms of it into account?
I thought that you were going to do that:
I’m happy to entertain objections from anyone, including you and Plantinga, as long as they are specific.
Says the man who has peppered this thread with comments like
…and “complimented” me on “keith’s incredible one-day mastery of modal logic”.
If you can’t take it, then don’t dish it out, Walt.
There’s a simple way for you to cut this “know-all” engineer, who presumes to instruct the Great Walto on de re and de dicto, down to size.
Show me where and why my argument fails. Be specific; no hand-waving.
To borrow one of your favorite taunts: Man up, Walt.
Can’t take it?! Don’t be absurd! (Or if it’s modesty, please don’t be so modest; I mean I know how modest you generally are.)
In point of fact, I’m extremely grateful both to you and to Gregory for pointing out my intellectual and behavioral infirmities, which are obviously both myriad and quite serious. But who wouldn’t be thankful for such a service–especially when freely and frequently provided? You two make an excellent team of critics that any site like this is really fortunate to have!
It will be interesting to see what objection walto tries next.
In the meantime, I promised to explain Plantinga’s argument (and its flaw) in terms of symbolic logic, so here goes.
ETA: I’m using a black diamond for the possibility operator instead of the standard white diamond, because the latter does not display properly on my tablet.
1. Let A be the property “is the real Alvin”. In other words, let Ax be true if x is the real Alvin but false otherwise. If dualism is true, for example, then Ax is false when x is Alvin’s body, but true when x is Alvin’s soul, because Alvin’s soul is “the real Alvin” under dualism.
2. Let P be the property “can continue to exist without Alvin’s body.” Px is obviously false when x is Alvin’s body.
3. Plantinga asserts that “it’s possible that Alvin could exist without Alvin’s body”. By itself, that statement is ambiguous. It admits of two interpretations (a) and (b), expressed below using logic notation:
a) ∃x(Ax ∧ ◆Px)
Reading left to right, this translates to “there is a particular x for which it is true that x is the real Alvin and x can possibly exist without Alvin’s body.”
Note that this statement can only be true if x is not Alvin’s body. In other words, we must assume that physicalism is false in order to make this statement true. Plantinga is trying to prove that physicalism is false, so he obviously doesn’t want to assume it, because then he’d be assuming his conclusion.
b) ◆(∃x(Ax ∧ Px))
Reading left to right, this translates to “it is possible that an x exists for which it is true that x is the real Alvin and x can exist without Alvin’s body”.
Unlike interpretation (a), this one does not require us to assume that physicalism is false, so this is the interpretation Plantinga must use in order to avoid begging the question.
Note that for interpretation (a), the possibility operator ◆ is applied directly to Px. That means that ◆Px is a modal property of x itself. In other words, the reference is de re, or “of the thing” itself.
For interpretation (b), the possibility operator applies to the entire statement ∃x(Ax ∧ Px). That means that it is a modal property of the statement, not of x itself. In other words, the reference is de dicto, or “of the statement”.
(Walt’s error here was to take de dicto literally, as if it applied to the English statement itself. It doesn’t. De dicto is meant logically, not literally, and it depends on the logical interpretation of the English statement.)
Since interpretation (b) is de dicto, Leibniz’s Law is not applicable. Plantinga plunges ahead and uses Leibniz’s Law anyway, yielding an unsound conclusion.
Unlike interpretation (a), this one does not require us to assume that physicalism is false, so this is the interpretation Plantinga must use in order to avoid begging the question.
Great “argument” that yours has finally morphed into over the course of this gigantic thread, keith!
To wit: “Plantinga is an astonishingly lame idiot, but he would never (NEVER!) beg a question. That’s how I know he confused de dicto and de re references in his argument, even though this distinction was largely brought to the attention of 20th Century philosophers by Plantinga.” Bravo.
PS. This is my second-to-last response to any of your posts, keith. You definitely deserve one more for your recent absolute classic of sophomoric sophistry and lack of intellectual integrity (in spite of not having all the pretty little pictures that your above post has) on the other thread.
walto, attempting to “paraphrase” part of my argument:
I haven’t called Plantinga an “astonishingly lame idiot” or even labeled him as stupid. It’s all in your head, Walt.
Instead, I’ve defended him:
walto:
I’m not claiming that Plantinga would “never (NEVER!) beg a question” or assume a conclusion. I’m just saying that he wouldn’t want to:
I’m giving Plantinga the benefit of the doubt. Assuming your conclusion is an error that every freshman philosophy student knows about. Mistaking de dicto for de re and/or misapplying Leibniz’s Law is a much more respectable error to make.
It’s odd that you want to accuse Plantinga of the stupider mistake, since you’ve supposedly been trying to defend his competence throughout this thread.
I repeat my challenge: