亞當斯論題與指示條件句的三值語意論

Adams' Thesis and Three-valued Semantics for Indicative Conditionals

亞當斯論題宣稱指示條件句「如果 A，B」的機率是條件機率P(B│A)，許多學者認為這個論題在直覺上是成立的，但對其明確意義及為何成立，則有不同的立場。本文將論證，亞當斯論題不僅僅是一個關於指示條件句的假說或假定，而且還可以基於指示條件句的三值語意學下，被恰當地說明及導出。本文首先說明史東內克對亞當斯論題的立場是難以成立的；其次論證傑克森對條件句的語意學難以提供對亞當斯論題的恰當說明；最後，基於條件句的三值語意論，提出一個對亞當斯論題的恰當理解方式。

“Adams' thesis” is that the probability of indicative conditionals is the conditional probability of the consequents given the antecedents. Many scholars believe that Adams' thesis is intuitively correct, but they disagree on its exact meaning and why it is correct. This paper argues that Adams' thesis is not only a hypothesis, but also one that can be properly explained and derived by an appropriate semantics of indicative conditionals. I shall first show that Stalnaker's interpretation of Adams' thesis is hardly correct, and that Jackson's semantics for indicative conditionals cannot provide a proper explanation and derivation for Adams' thesis. Finally, I argue that McDermott's 3-valued semantics for indicative conditionals is on the right track to account for Adams' thesis. Based on McDermott's work, I further provide a generalized probability theory of 3-valued indicative conditionals, and given the generalized probability theory it shall be shown that Adams' thesis can be properly explained and derived as a special case when the indicative conditionals under consideration are simple indicative conditionals.