ec429 comments on Arguing "By Definition" - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (38)
Would it be accurate, then, to say that any valid use of "by definition" can be replaced by "a fortiori"?
As in, "Socrates is a [mortal, featherless, biped]. Therefore a fortiori Socrates is mortal." is valid (though one might dispute the premise). But "Socrates is a [featherless, biped]. Therefore a fortiori Socrates is mortal." is plainly obviously nonsense, even to people who think they can argue "by definition!". The remaining problem, of course, being that not everyone accepts that a fortiori deserves the certainty that they have been claiming for by definition!.
(In classical logic, if A∧B, then a fortiori A. In Bayescraft, P(A) >= P(A∧B) a fortiori)