[請益] 什麼是有效推論?
1.在"大師不敢翹的課"一書中說:論証的有效性有語句的真假是兩回事。
有效性是指論証結構有效。
2.但是我查到關於有效論証的定義是:前題為真的時候,結論不能為假。
請看下面的例子
if 16 is divided by 4, then 16 is divided by 2
16 is divided by 2
so, 16 is divided by 4
由 1. 這個論証結構是無效的,所以是一個無效論証 (invalid argument)
由 2. 這個論証的前題都為真,結論也為真,所以是一個有效論証 (valid argument)
是哪裡搞錯了?
thanks
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