Seems like people missunderstood the type of riddles Matias was looking for. I think he looks for riddles where you put forward a number of claims and the listener agrees to each of them but the end result is totally illogical.

I can't remember the exact wording, but one goes something like this:

You have ten persons and only nine rooms. Put the extra person together with the person in room 1 for now.

The third person goes to room 2.
The fourth person goes to room 3.
The fith person goes to room 4.
The sixth person goes to room 5.
The seventh person goes to room 6.
The eighth person goes to room 7.
The ninth person goes to room 8.

That leaves room number 9 empty so you can have the tenth person from room number 1 walk into this room instead. So this way you have fitted ten people in nine rooms.


Paul Curry made this into a real magic trick by using gaffed cards with pictures of magicians and hats. It was all illustrated with the cards as the story went along.

Would be great hearing more riddles like this one.

/Tomas

Although not technically a riddle, Hempel's paradox of the raven is an interesting mind-melter.

Consider the statement:

All ravens are black.

A logical equivalent to this statement (the contrapositive) would be: All non-black objects are non-ravens.

So, lets say you walk around looking for evidence of your claim. Every time you saw a non-black object, like a yellow car for instance, it would be a confirming instance of the claim that all non-black objects are non-ravens, and therefore a confirming instance of the claim that all ravens are black.

There are 2 things "wrong" with this though.

The first is, how is it possible that seeing a yellow car is a confirming instance that all ravens are black? I mean, what does one have to do with the other?

And two: Wouldn't seeing that yellow car also be a confirming instance of the statement, "All ravens are red"? How can something be a confirming instance of two contradictory claims?

Strange...

Jason

Re: All ravens are black. ... A logical equivalent to this statement...

Such is why the ANCIENT Greeks took the trouble to write the basics of what we call symbolic logic down into books.

It helps to read... lest all be as you described: strange.

For the lazy... if "all A are B" is taken as true, then one can infer that "if X is not B, then X is not A". In this case, if X is a bird that is not Black, then X is not a Raven.

Those that snicker about albino Ravens are excused from the class. Such people tend to slow the learning of others.

Mr Townsend wrote:
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if "all A are B" is taken as true, then one can infer that "if X is not B, then X is not A". In this case, if X is a bird that is not Black, then X is not a Raven.
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That translates directly to: if X is not black, then X is not a raven. No need to strengthen the condition to say that X has to be a bird. The trick is to realize that there is _no_ flaw in what Jason wrote although the result sounds highly illogical.

/Tomas

Tomas is, as usual correct.

I was trying to both write out the steps and work in ordinary English, and got tripped up by the image of an albino raven... excuse me

Logically correct statements sometimes sound irrational and counterintuitive.

All horses have an infinite number of legs. Here's why.

A horse has forelegs at the front and two hind legs at the back.

4 + 2 = 6

So a horse has six legs. But six is an odd number of legs for a horse to have. But a horse has an even number of legs.

So a horse can't have both an even number of legs and an odd number of legs.

Unless.....

.....the only number that is both even and odd is infinity.

Therefore a horse has an infinite number of legs.

QED

Dave