On Jul 13, 2005, at 12:48 AM, [EMAIL PROTECTED] wrote:
> Consider the following line of reasoning. Let p be the proposition
> "Ronald was born in New York." From p, we can infer q: Ronald was
> born in the United States. From q, we can infer r: It is possible
> that Ronald was born in New Jersey. On the other hand, from p we
> can infer s: It is not possible that Ronald was born in New Jersey.
> We have arrived at a contradiction. What is wrong? Note: To answer
> the question, familiarity with modal logic is not needed.
to me, inferring r from q alone is wrong as you forgot that p still
holds.
(p AND p->q) -> (q AND NOT r)
- Umberto Straccia
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