- 19 May '12 00:46Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that
*modus tollens*is a valid form of argument:

P -> Q

Not-Q.

Therefore, not-P.

So, then, here is the proof:

(1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.

(2) I am not evil.

(3) Therefore, God exists.

- 19 May '12 01:10

Except that (2) is not the same as the consequent of (1). If I am not evil, then the conditional 'If I am not evil, I will be punished after I die' is trivially true. It's not modus tollens.*Originally posted by LemonJello***Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that***modus tollens*is a valid form of argument:

P -> Q

Not-Q.

Therefore, not-P.

So, then, here is the proof:

(1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.

(2) I am not evil.

(3) Therefore, God exists.

- 19 May '12 01:13 / 3 edits

I think you made a typo in the antecedent of your conditional.*Originally posted by Conrau K***Except that (2) is not the same as the consequent of (1). If I am not evil, then the conditional 'If I am not evil, I will be punished after I die' is trivially true. It's not modus tollens.**

At any rate, it is*modus tollens*. Take another look at the full consequent of (1). - 19 May '12 01:17

http://i0.kym-cdn.com/photos/images/original/000/131/351/eb6.jpg?1307463786*Originally posted by LemonJello***Before I present the proof, recall the following. P -> Q is true whenever P is false or Q is true. Recall also that***modus tollens*is a valid form of argument:

P -> Q

Not-Q.

Therefore, not-P.

So, then, here is the proof:

(1) If God does not exist, then it is not the case that if I am evil, I will be punished after I die.

(2) I am not evil.

(3) Therefore, God exists.

- 19 May '12 01:28 / 1 edit

the only mystery about the "proof" is whether you thought of it as a joke(aka trolling) or you had a brain fart (aka stupid) and you actually believe you came up with something intelligent.*Originally posted by LemonJello***Tell me precisely what is wrong with the proof. I know what the problem is here; do you?**

either way, it is illogical. - 19 May '12 01:31

If it is illogical, then please point out where the logic fails.*Originally posted by Zahlanzi***the only mystery about the "proof" is whether you thought of it as a joke or you had a brain fart and you actually believe you came up with something intelligent.**

either way, it is illogical.

Anyway, I did not come up with this proof. A person much smarter than I came up with it. I think it can be an instructive exercise to try to figure out why it fails. - 19 May '12 01:40

instructive exercise? for something this poorly constructed? are you kidding?*Originally posted by LemonJello***If it is illogical, then please point out where the logic fails.**

Anyway, I did not come up with this proof. A person much smarter than I came up with it. I think it can be an instructive exercise to try to figure out why it fails.

i ask again, are you trolling? the alternative to this might be more embarrassing for you. - 19 May '12 01:41

I repeat: if it is illogical, then please point out where the logic fails. And please be specific.*Originally posted by Zahlanzi***instructive exercise? for something this poorly constructed? are you kidding?**

i ask again, are you trolling? the alternative to this might be more embarrassing for you. - 19 May '12 01:46

i fed the troll. i am ashamed.*Originally posted by LemonJello***I repeat: if it is illogical, then please point out where the logic fails. And please be specific.**

please feel free to congratulate yourself for provoking me into 3 posts in a trolling thread.

or feel free to assume i am ignorant of logic and jealous of your awesome intellect if you are sincere in wanting to debate this. - 19 May '12 01:49

So you are unwilling (or unable) to back up your claim that the proof I presented is illogical?*Originally posted by Zahlanzi***i fed the troll. i am ashamed.**

please feel free to congratulate yourself for provoking me into 3 posts in a trolling thread.

or feel free to assume i am ignorant of logic and jealous of your awesome intellect if you are sincere in wanting to debate this.

You get a FAIL. - 19 May '12 02:01 / 2 edits

Basically what I mean to say is that the conditional is trivially false and modus tollens does not apply.*Originally posted by LemonJello***I think you made a typo in the antecedent of your conditional.**

At any rate, it is*modus tollens*. Take another look at the full consequent of (1).

As I see it, there are three propositions:

P -- God exists

Q -- I am evil

R -- I will be punished after I die.

So the proof runs like this:

(1) ~P --> ~(Q-->R)

(2) ~Q

Therefore,

(3) P.

If ~Q, however, then Q-->R is trivially true, so the consequent ~(Q-->R) is trivially false.

Under the same logic, you can mount a proof of anything. Basically it's a failure of relevance logic, like saying 'If the world will end, then 2+2 =4'. - 19 May '12 02:14 / 3 editsSo, as far as propositional calculus goes, it is logical.

Reductio ad absurdum:

(1) ~P --> ~(Q-->R)

(2) ~Q

Therefore,

(3) ~P. (i.e. God does not exist)

From (1)

~~P or ~(Q-->R)

so,

P or (Q and ~R)

But (Q and ~R) contradicts (2) ~Q.

But P contradicts (3) ~P.

I think the failure must be relevance, the fact that we are dealing with truth triviality. We get the same triviality if we assert R, I will be punished after I die. So if I will be punished after I die, then (Q-->R) is trivially true and so ~(Q-->R) false and therefore ~P is false, so P, God must exist. - 19 May '12 02:20 / 1 edit

Yes, very good. You've proven yourself much more worthy than our friend Zahlanzi.*Originally posted by Conrau K***Basically what I mean to say is that the conditional is trivially false and modus tollens does not apply.**

As I see it, there are three propositions:

P -- God exists

Q -- I am evil

R -- I will be punished after I die.

So the proof runs like this:

(1) ~P --> ~(Q-->R)

(2) ~Q

Therefore,

(3) P.

If ~Q, however, then Q-->R is trivially ...[text shortened]... asically it's a failure of relevance logic, like saying 'If the world will end, then 2+2 =4'.

I do not think the problem here involves any mis-application of*modus tollens*. But I would agree that the problem is related to the subject of relevance logic. The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional. - 19 May '12 02:23
*Originally posted by LemonJello***Yes, very good. You've proven yourself much more worthy than our friend Zahlanzi.**

I do not think the problem here involves any mis-application of*modus tollens*. But I would agree that the problem is related to the subject of relevance logic. The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional.**The problem here must lie in how it treats an indicative conditional like 'If I am evil, I will be punished after I die' and bases it in the truth functionality of a material conditional.**

Yes, that sums it up. It was nothing to do with modus tollens per se. Thank you for that interesting piece of logic.