What the Tortoise Said to Achilles

  • Thread starter Thread starter murshid_islam
  • Start date Start date
AI Thread Summary
The discussion centers on Lewis Carroll's "What the Tortoise Said to Achilles," questioning the logic and perceived paradox within the text. Participants explore whether there is a logical error, concluding that the story illustrates the necessity of accepting foundational rules of logic to evaluate propositions. The term "paradox" is debated, with some participants noting its classification as the Carroll paradox in various literature. There is a consensus that the story does not present a clear contradiction but rather highlights the complexities of logical inference. The conversation emphasizes the importance of understanding the foundational axioms in logic and mathematics.
murshid_islam
Messages
468
Reaction score
21
"What the Tortoise Said to Achilles"

"What the Tortoise Said to Achilles" by Lewis Carroll: http://www.ditext.com/carroll/tortoise.html

What exactly is wrong with the logic here? Is anything wrong at all?
 
Physics news on Phys.org


No error. It is just noting that in order to accept any logical proposition as true, you must first accept the "rules of logic" as true. And, in order to do that, you must accept the rules used to construct those rules, etc.

That is why mathematical logic (I can't speak for philosophers) always starts with "given" rules and axioms.
 


Also see the Wikipedia article on this topic.
 


I don't understand what makes this story paradoxical. Can anyone enlighten me as to where there is a contradiction or otherwise?
 


I see nowhere any mention of "paradox". Where did you get the idea that the story was "paradoxical"?
 


Wikipedia refers to it as the Carroll paradox. It is included in Micheal Clark's book Paradoxes from A to Z as the Paradox of Inference. Thus I get the idea that the story was paradoxical.
 
I'm taking a look at intuitionistic propositional logic (IPL). Basically it exclude Double Negation Elimination (DNE) from the set of axiom schemas replacing it with Ex falso quodlibet: ⊥ → p for any proposition p (including both atomic and composite propositions). In IPL, for instance, the Law of Excluded Middle (LEM) p ∨ ¬p is no longer a theorem. My question: aside from the logic formal perspective, is IPL supposed to model/address some specific "kind of world" ? Thanks.
I was reading a Bachelor thesis on Peano Arithmetic (PA). PA has the following axioms (not including the induction schema): $$\begin{align} & (A1) ~~~~ \forall x \neg (x + 1 = 0) \nonumber \\ & (A2) ~~~~ \forall xy (x + 1 =y + 1 \to x = y) \nonumber \\ & (A3) ~~~~ \forall x (x + 0 = x) \nonumber \\ & (A4) ~~~~ \forall xy (x + (y +1) = (x + y ) + 1) \nonumber \\ & (A5) ~~~~ \forall x (x \cdot 0 = 0) \nonumber \\ & (A6) ~~~~ \forall xy (x \cdot (y + 1) = (x \cdot y) + x) \nonumber...
Back
Top