Johnicholas comments on Making your explicit reasoning trustworthy - Less Wrong

82 Post author: AnnaSalamon 29 October 2010 12:00AM

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Comment author: AlanCrowe 29 October 2010 08:37:10PM *  3 points [-]

Propositional calculus is brittle. A contradiction implies everything.

In Set theory, logic and their limitations Machover calls this the Inconsistency Effect. I'm surprised to find that this doesn't work well as a search term. Hunting I find:

One page

In classical logic, a contradiction is always absurd: a contradiction implies everything.

Another page

Another trouble is that the logical conditional is such that P AND ¬P ⇒ Q, regardless of what Q is taken to mean. That is, a contradiction implies that absolutely everything is true.

Any false fact that you believe acts as a logic bomb. Once you come across the true fact, the combination permits you to construct a logical argument to reach any conclusion. This is just what the monsters from the Id have been waiting for.

The inconsistency effect implies that fallible creatures dare not rely on pure logic.

Comment author: Johnicholas 29 October 2010 08:42:42PM 2 points [-]

"Ex falso quodlibet" or "principle of explosion" might be the search term you are looking for. Relevance logic and other nonclassical logics are not explosive in the same way.