意志軟弱與實踐理性──一個戴維森式的進路

Abstract

本論文主要處理兩個關於意志軟弱的問題。第一個問題是：意志軟弱到什麼層面上是可能的? 第二個問題是：意志軟弱的問題為何? 這兩個問題直到戴維森《意志軟弱如何可能?》一文出版以後才引起廣泛討論。在此文中，戴維森提出了兩個主張。首先他主張因為違反出於全面考量的評價判斷的意圖行動是可能的，因此意志軟弱是可能的。其次，他主張意志軟弱是實踐不理性的典型。前述兩個問題即是針對戴維森這兩個主張的挑戰。然而戴維森從未直接回應過這些挑戰。本文的目標就是要藉由建立一個戴維森式的進路來替戴維森提出完整的回應。本論文將立基於戴維森所提出的關於意志軟弱、意圖行動、行動理由、實踐理性的主張，並援引近期相關議題的討論來建立一個戴維森式的進路。 在第一章中我將闡述戴維森的因果行動理論，以及戴維森如何修改此理論使其能與意志軟弱相容。在第二章中我藉由戴維森對評價與語言之基本關係的檢視，來建立一個支持判斷內在論的戴維森式評價判斷理論。接著在第三章中我論證為何嚴格的意志軟弱是不可能的。這兩章的討論將能回答關於意志軟弱的第一個問題。在第四章中我將藉由探討行動理由是什麼來辯護一個戴維森式的立場--意志軟弱必定是實踐不理性。在第五章中我主張一個良好的實踐理性理論必須要能夠解釋實踐不理性，並分析幾個常見的實踐理性理論，最後我論證只有戴維森式的理論能夠恰當地解釋意志軟弱的實踐不理性。 本論文中的討論立基於四個非常符合直覺且被廣泛接受的預設。第一個預設是意圖行動的標準觀點，此觀點認為意圖行動就是有理由的行動。第二個預設是意志軟弱是意圖行動。第三個預設是意志軟弱是實踐不理性的行動。第四個預設是理由立基於理性。本論文的結論是，如果我們接受這四個預設，則我們必定接受一戴維森式的觀點—行動理由的構成必須扮演兩個不同的角色以解釋實踐不理性。

This dissertation concerns two main questions about weakness of will. The first question is: “To what extent is weakness of will possible?”. The second question is: “Must weakness of will be practically irrational?”. This dissertation is thus divided into two parts, corresponding to these two questions. These two questions did not emerge until the publication of Donald Davidson’s influential paper “How is Weakness of the Will Possible?”, in which Davidson argues for two theses. Firstly, he argues that weakness of will is possible because it is possible to act intentionally against one’s all things considered evaluative judgment. Secondly, he argues that weakness of will is a paradigm of practical irrationality. The aforementioned two questions are raised by the critics of Davidson as challenges to these two theses. However, Davidson has never directly offered full responses to the challenges. This dissertation thus aims to offer a complete reply on behalf of Davidson by constructing a Davidsonian approach. The approach is Davidsonian because I will stick to Davidson’s main theses regarding weakness of will, intentional action, and practical rationality, while my arguments may appeal to resources found in recent two decades. In Chapter 1, I give an overview of Davidson’s causal theory of action and how Davidson amends it to cope with the possibility of weakness of will. The aim of this chapter is to lay sufficient groundwork for discussions in the following chapters. Chapter 2 and 3 are devoted to answering the first question. In Chapter 2, I reconstruct a Davidsonian theory of evaluative judgment in order to defend judgment internalism in virtue of resources found in Davidson’s investigation of the basic relation between evaluation and language. I focus on the question about why strict akrasia is impossible in Chapter 3. In Chapter 4 and 5 I then take up the issue about whether weakness of will is paradigmatically irrational. In Chapter 4, I defend the Davidsonian position that it must be irrational in virtue of a study of practical reasons. In Chapter 5, I scrutinize several theories of practical reason and argue that only the Davidsonian approach can offer satisfactory explanation to the practical irrationality of weakness of will. Discussions in this dissertation are based on four intuitive and widely accepted assumptions. First of all, I assume the standard conception of intentional action, the view that an intentional action is an action done for a reason. Secondly, I assume that a weak-willed action is an intentional action. Thirdly, I assume that weakness of will is must be practically irrational. My last assumption is that reasons for action are grounded on practical rationality. I conclude that if we accept these four assumptions altogether, we must accept the Davidsonian view that a practical reason must play two different roles in order to explain the irrationality of weakness of will—that it serves as a reason that explains the intentional dimension of a weak-willed action and that it serves as a cause that explains the irrational dimension of it.