Who Watches The Watchmen?

Logic Level 3

(1) Both sentences in this box are false. (2) Superman exists. \begin{array}{|l|} \hline \small{\text{ (1) Both sentences in this box are false. }} \\ \small{\text{ (2) Superman exists. }} \\ \hline \end{array}

If these statements are both logical, then does Superman exist?

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20 solutions

Ivan Koswara
Jan 23, 2016

If the first statement is true, it implies both statements are false; in particular, the first statement is false. This is a contradiction. So the first statement is false, so not both statements are false. This means at least one of the statements is true. Since the first statement is false; this gives the only other option of the second statement being true; that is, Superman exists.

A variant of this is Curry's paradox : statements in the form "If this sentence is true, then P" always implies P is true. (To compare with this problem, this problem has the form "(1) Both statements are false, (2) P", which also implies P is true.)

I believe this is related to the principle of explosion. XKCD made a lovely comic on this showing how you, too, can derive your friend's mum's phone number from two contradictory axioms.

Chris Watts - 5 years, 4 months ago

Who have watched the movie? Superman does exist.

Evan Huynh - 5 years, 4 months ago

Superman does not exist and I got it wrong.

yera kim - 5 months, 2 weeks ago
Colin Carmody
Jan 19, 2016

Well, the box as a whole could be false. Just because the box says something, doesn't make it true!

Ok, my solution is to start by saying both statements are false (guess and check). But if they are both false, then 1 would be true. If 1 is true, then 1 can't be false.

So now try making both true. But if both are true, 1 must be false. But this works because 1 is false (because they are not both false) because 2 is true. So then apparently superman is real. Though we really know he isn't because who trusts some random box!

A slight variation: If (1) is true then it must also be false, which is a logical non sequitur. If (1) is false then at least one of the statements in the box must be true, and since (1) is false, statement (2) must be true.

Brian Charlesworth - 5 years, 4 months ago

If the first statement is false the second is true. If the first statememt is true the second is false. I do not see how the second can be always true.

Zamir Manaj - 5 years, 4 months ago

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Correct, but you can see in the question, it is written outside of box, if these statements are perfectly logical, and therefore Statement 2 is correct.

Akshat Mehra - 5 years, 4 months ago

If 1 is false, it does not matter that it claims to be true together with number 2. So 2 does not have be true. Nothing can be proven (in the rectangle, not a box, see Hydrogen Pc below) about Superman .

Bent. O. Jensen - 5 years, 4 months ago

This is something we call a "paradox". I'm surprised there were only two options, out of which neither is correct.

If the statement had been, "If these statements are perfectly logical, then do they imply that Superman exists?" then it would have been true. However, just because the argument is valid doesn't mean it's conclusions are actually true. As I read the question, it went something like "Given the statements in this box, does Superman actually exist?". Clearly the answer to this is false; you can't just define things into actual existence from logical statements.

Adam Morgan - 5 years, 4 months ago

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You haven't met my wife.

Anthony Locascio - 5 years, 4 months ago

If 1 is false, why does 2 have to be true?

Stephen Hurlbut - 5 years, 4 months ago

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If 1 is false, 2 can't be false too: because then both statements in the box are false, which means 1 is true, not false.

Alex Bean - 5 years, 4 months ago

Logically, these statements are problematic The first statement hinges on the veracity of the second. The second statement has no relevancy to the first statement.

As such, the statements are not logical

Add to that the fact that Superman (as an idea) does exist.

Christopher Felch - 5 years, 4 months ago

Exactly! Let's say the box is true and both sentences are true; therefore: Both sentences are false, hence: Superman does not exist and ○ Both sentences are true, hence: Superman does exist and ● Both sentences are false, hence: etc.

Alistair Bailey - 5 years, 4 months ago
Jonathan Grant
Jan 24, 2016

Everyone is giving solutions based on whether the statements are true or false, but the question only asks if they are logical. The first statement is logical as it says both sentences in the box are false. However only one sentence in the box is false, the first one. This would make the first statement false (meaning both the statements in the box aren't false) allowing the second to be true.

Hydrogen Pc
Jan 24, 2016

A box is a 3 dimensional object...therefore the first statement doesn't count.

Best proof.

Bent. O. Jensen - 5 years, 4 months ago
Jessica Moskowitz
Jan 24, 2016

The first point says "Both sentences in this box are false." Assuming that sentence is telling the truth, that would then make the sentence false, so we know that this statement is false. So, the truth in this statement becomes "Not both sentences are false," or "At least one sentence is true." Since we know the first sentence is false, that means that the second sentence, "Superman exists," must be true. So, Superman exists.

Elyse Zois
Jan 24, 2016

The first statement can't be true because it says both statements are false, implying that it is false.Since it is false, the other can't be false also because that would make the first statement true. So the second statement is true and Superman exists.

Rohit Chipper
Jan 23, 2016

A slight variation: If (1) is true then it must also be false, which is a logical non sequitur. If (1) is false then at least one of the statements in the box must be true, and since (1) is false, statement (2) must be true.

Josh Edwards
Mar 21, 2016

This is somewhat a paradox, but simple to understand. If the first statement is false, which cancels itself out, means the second sentence is still valid.

Example: this is not, not superman. A double negative cancels the first negative, that's how I see the problem anyway.

Pawin Vongmasa
Jan 31, 2016

I made the correct guess of what the asker might have in mind, but this question is really badly formed. What does "if these statements are perfectly logical" mean?

To those who have answered "correctly", is your answer based on statement (1) being false? Mine is, and that's the problem. Is being false considered perfectly logical?

A better way to phrase this question is probably to ask "In a valid valuation, what is the truth value of statement (2)?"

Or more simply, "To make p ( ¬ p ¬ q ) p \leftrightarrow (\lnot p \land \lnot q) true, what truth value should be assigned to q q ?"

João Arruda
Jan 26, 2016

The sentences cannot have the same logical value, as the first one is stating FALSE both of them, so we know that they have opposite logical values.

Evaluating the first sentence, we have that, if true, both are false, which causes a paradox. For it to be perfectly logical, the first sentence needs to be false, automatically setting the second one to true.

Adi Garg
Jan 25, 2016

the question says that both the statements in the box are false hence the first statement is itself a false one...... this leads to the conclusion that statement number two is correct

Nathaniel Hoffman
Jan 24, 2016

One way you could think about this is that "perfectly logical" doesn't mean true. It could just mean it's a well formed logical expression. The other way is that if the inverse of (1) is that at least one of the sentences are true. Both of the sentences being true results in a paradox, but one of them being true results in an infinite looping "paradox" where Superman always exists.

Tom Barber
Jan 24, 2016

Superman is real, because if argument 1 is false (both argument 1 and 2 are false) , then for it to be false, only one argument needs to be true. So, if superman does exist, it qualifies as the first argument being wrong.

if the first statement is true, then there is a paradox within the statement ( as it can not be true and false at the same time). That means the first statement is false, and for that to occur, at least one statement must be true, ergo (2) is true

Miksu Rankaviita
Jan 24, 2016

I don't know if this is a valid solution but I thought it like this:

(1) => ¬(¬(2)) ≡ (2)

Because first (1) negates (2) but then it negates itself so it should end up double negating (2)...

Akshat Mehra
Jan 24, 2016

Don't try to get confused. There is a hint itself in Statement 1 :- Both statements in this box are false. That means Statement 1 is itself false and so Statement 2 is true.

Debasis Rath
Jan 24, 2016

Well if I were any of u I would first see that is statement 1 is false this means that the possiblity of existaance superman increases also the sentences are completely logical hence the more appropriate option is yes superman exists

Austin Ginos
Jan 24, 2016

This was my logic, which probably isn't logically sound but it got me the correct answer. Nothing says only the first statement can be false, and upon assuming that, in order to keep it false then both statements cannot be false. Therefore the second statement must be true.

Brett Grothouse
Jan 24, 2016

The "if" portion of the statement is not true, there for the "then" portion is automatically true. Make a truth table with p, q, p->q. In both cases where p is false, p->q is true.

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