Re:A Simple Logical Puzzle That Shows How Illogical People Are
by ikeboy on Friday May 22, 2015 @04:44PM
(#9590827)
>The problem with this is that the 5 card also needs to be turned; it might have an even number on the back.
If you can't be sure that the cards have a color and a numbers, there's nothing outlawing a 5-6 card, which breaks (2).
Re:A Simple Logical Puzzle That Shows How Illogical People Are
by greggyb on Friday May 22, 2015 @04:56PM
(#9590873)
So if I understand correctly:
You trust that if a card has a color on one side, it has a number on the other side.
You do not trust that if a card has a number on one side, it has a color on the other side.
Is this correct?
Re:A Simple Logical Puzzle That Shows How Illogical People Are
by ikeboy on Friday May 22, 2015 @05:08PM
(#9590906)
No. I don't make any assumptions as to anything I can't see.
However, regardless of what's on the back of blue, (2) will still be correct; the consequent is true, therefore the conditional is true.
Re:A Simple Logical Puzzle That Shows How Illogical People Are
by greggyb on Friday May 22, 2015 @05:30PM
(#9590979)
Okay, I see where you're coming from now.
(1) may or may not be true. Understanding that we cannot trust (1), but that we don't care to verify it, then the 5 is necessary to prove (2).
That is much more subtle than I originally interpreted from you original post. Thanks for your patient explanation.
If you doubt (1), how is it that you need to verify that the 5 has a color, but not that the blue has a number on the other side?
To verify (2) you only need to prove that every even card has a blue back. An odd may be blue or green, but an even must be blue. Hence the 5 is fine, it can have any color. The blue is fine, because it can have any number. But that 8 must have a blue back, and that green must have an odd number.