Hugo Alves, <arcozelo@hotmail.com>, writes:
> If I say
> 1. All men are mortal.
> 2. John is a man.
> 3. Therefore John is mortal.
>
> what makes the third sentence true based on the previous two? You say it is
> logical, it is evident, but why is it so?
There is a very funny dialog about this by Lewis Carroll between Achilles
and the Tortoise. It's probably in Goedel, Eoscher, Baech. The Tortoise
is playing dumb with Achilles and making him explain syllogisms:
A. <whatever>
B. <whatever>
C. A & B -> Z
Given A and B, and that A&B->Z, Achilles explains that we have to
accept Z. The Tortoise refuses to accept this and makes Achilles
write it down as D:
D. A & B & C -> Z
"There!" says Achilles. "Now we're done. Given A and B and C and D,
you MUST accept Z!"
"Why?" asks the Tortoise.
"Because of Logic! Logic will MAKE you accept it. Logic will take
you by the throat and FORCE you to accept it!"
But the Tortoise insists that Achilles write it down, so he sadly
takes out his book and enters
E. A & B & C & D -> Z
"Good thing you've got plenty more pages in your book," the Tortoise
says cheerfully.
Hal
This archive was generated by hypermail 2b30 : Mon May 28 2001 - 09:56:46 MDT