※ 引述《staminafish (再見了)》之銘言：
: 1.If everyone promotes his/her own greatest good, then the greatest good
: for all will result.
: 2.We ought to promote the greatest good for all
: _______________________________________________________________________
: Everyone ought to promote his/her greatest good
: 請問這個論證為何是一個無效論證呢?
: 我唯一想到的可能是第一個前提丐題
: 但要如何修正才會成為一個有效論證呢?
: 請各位前輩告訴我
: 我想了很久想不出來> <
: 謝謝
The problem is partly from the concept of obligation(ought to) is not a
suitable concept for the standard formalization of first order logic. Let
OUG- be the modal operator stand for "It ought to be the case that...",
(moral necessity), we can formalize the argument as following:
If P then Q
OUG-Q
___________________
OUG-P
Is this a valid argument?
Sry I am tired, lets talk tomorrow..................
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