非單調推論及預建：評洛特之反例

Nonmonotonic Reasoning and Defaults: On Rott's Counterexamples

此篇論文旨在以萊特於1980年所提出的預建邏輯系統，消除洛特對AGM理論的單調性原則提出的反例。相較於古典邏輯，雖然AGM理論主張知識狀態具備均衡性，並建構基本函映的預設說明信念變遷，但是許多哲學家認為該理論有某些基本原則值得質疑，洛特即指出AGM理論主張原有知識狀態的某個信念弱化之後，並不會影響原知識狀態的單調性並不成立。然而，洛特的反例之所以成立，在於可能出現相同語句卻具有不同資訊價值的情況，不過，洛特也並未提出適當的方式說明處理非單調的信念變遷過程。因此，我在這篇論文中要以AGM理論結合預建邏輯的方法消除洛特提出的反例，亦即主張在AGM理論中加入預建邏輯的推論規則，可以適當地處理非單調的信念變遷過程。 This paper aims to dissolve Rott's counterexamples in terms of default logic proposed by Reiter in 1980. In his counterexample, Rott pointed out that some fundamental principles in AGM theory which meet the property of monotonicity are implausible because it seems unable to handle the processes of nonmonotonic reasoning which are common in our ordinary reasoning. In contrast to classical logic, AGM theory indeed developed a prominent way to deal with belief change, whereas many philosophers still casted doubts on the fundamental principles in AGM theory. For example, there might be some sentences in one's belief set which are of the same form but different in information value and AGM theory does not commit it. Nevertheless, Rott failed to suggest a plausible way to fix the defect of AGM theory, so I aim to propose a suitable way to dissolve the problem of the processes of nonmontonic reasoning in virtue of the association of AGM theory with default logic.