Reasons as Defaults

John F. Horty

Provides a precise, concrete account of reasons and their interaction, based on the logic of default reasoning

Reasons as Defaults

John F. Horty

Description

Although the study of reasons plays an important role in both epistemology and moral philosophy, little attention has been devoted to the question of how, exactly, reasons interact to support the actions or conclusions they do. In this book, John F. Horty attempts to answer this question by providing a precise, concrete account of reasons and their interaction, based on the logic of default reasoning. The book begins with an intuitive, accessible introduction to default logic itself, and then argues that this logic can be adapted to serve as a foundation for a concrete theory of reasons. Horty then shows that the resulting theory helps to explain how the interplay among reasons can determine what we ought to do by developing two different deontic logics, capturing two different intuitions about moral conflicts.

In the central part of the book, Horty elaborates the basic theory to account for reasoning about the strength of our own reasons, and also about the related concepts of undercutting defeaters and exclusionary reasons. The theory is illustrated with an application to particularist arguments concerning the role of principles in moral theory.

The book concludes by introducing a pair of issues new to the philosophical literature: the problem of determining the epistemic status of conclusions supported by separate but conflicting reasons, and the problem of drawing conclusions from sets of reasons that can vary arbitrarily in strength, or importance.

Reasons as Defaults

John F. Horty

Introduction

I Default logic
1 A Primer on Default Logic
1.1 Basic concepts
1.1.1 Default rules
1.1.2 Priority relations
1.1.3 Theories and scenarios
1.2 Central definitions
1.2.1 Binding defaults
1.2.2 Proper scenarios and extensions
1.3 Extensions and conclusions
1.3.1 Theories with multiple extensions
1.3.2 Theories without extensions

2 From Defaults to Reasons
2.1 An austere theory of reasons
2.2 Developing the theory
2.2.1 Conflict, strength, and defeat
2.2.2 Reasons and enablers
2.2.3 Reason amalgamation

II Deontic Logic
3 Reasons and Oughts
3.1 The two logics
3.1.1 Simple oughts
3.1.2 Conditional oughts
3.1.3 Some history
3.2 Properties of the logics

4 Moral Conflicts
4.1 Logical objections
4.1.1 Agglomeration
4.1.2 Other logical objections
4.2 Conceptual objections
4.3 Objections based on reasons as moral forces

III Some Elaborations
5 Variable Priorities and Exclusion
5.1 Variable priority default theories
5.1.1 The definition
5.1.2 Some examples
5.2 Exclusionary default theories
5.2.1 The definition
5.2.2 Some examples
5.3 Discussion
5.3.1 Downward closure of exclusion
5.3.2 Exclusion by weaker defaults
5.3.3 Excluders, intensifiers, and attenuators

6 Particularism
6.1 Dancy's argument
6.2 Evaluating the argument
6.3 Discussion
6.3.1 Pragmatic considerations
6.3.2 Borrowing a book
6.3.3 Moderate particularism

IV Some complications
7 Skepticism and Floating Conclusions
7.1 Floating conclusions
7.1.1 Arguments and paths
7.1.2 Two versions of skepticism
7.2 The problem with floating conclusions
7.2.1 An example
7.2.2 Objections to the example
7.3 Discussion
7.3.1 Other examples
7.3.2 Skepticism

8 Problems with Priorities
8.1 Refining the concept of defeat
8.2 Controlling the order of application
8.3 Discussion
8.3.1 Inappropriate equilibria
8.3.2 Other orderings
8.3.3 Reinstatement

V Appendices
A Notes on the default logics
A.1 Proper scenarios
A.2 Some observations on defeat
A.3 Normal default theories
B Notes on the deontic logics
B.1 A comparison with van Fraassen's logic
B.2 A comparison with standard deontic logic

Reasons as Defaults

John F. Horty

Author Information

John F. Horty is Professor of Philosophy, University of Maryland. He is the author of Agency and Deontic Logic and Frege on Definitions.

Reasons as Defaults

John F. Horty

Reviews and Awards

"The beauty of this book is that while at the same time it opens unexpected and challenging complexity in familiar problems, it provides tools to master this complexity with a sense that an outcome of permanent value has been accomplished. In doing so, it takes the philosophy of normative reasoning to a new level, and, I think, provides some hope that this sort of clarity can be preserved even as the scope of the theory is widened." --Richmond H. Thomason, Notre Dame Philosophical Reviews

"Through Horty's lucid and elegant development of the logic of default reasoning we are presented with strikingly new applications to philosophical issues. Deontic logic is taken out of its Procrustean bed in possible world semantics, the debates over moral dilemmas and particularism in ethics are transformed. This is truly an eye-opening book." --Bas van Fraassen, Princeton University and San Francisco State University

"The notion of a reason is a basic part of the way in which we understand the world and our place in it. Until now, like others, I have taken the view that this notion cannot be analysed; at best it can be explicated in terms of considerations that favour responses. Horty's book shows that my pessimism was premature: a reason is a premise of a triggered default rule. This is a notable contribution, one which anyone who wants to understand reasons will need to address." --Jonathan Dancy, University of Reading and University of Texas

"This is a beautiful, elegant book. It should be required reading for anyone serious about thinking rigorously about ethics. According to a now-orthodox conception, what we ought to do is a product of the interaction of our reasons for different options. But very little serious work has been done on how reasons come together to determine what we ought to do, and much of that has been naive. In this fascinating and deep book, Horty shows how to use the resources of default logic in order to think rigorously about how reasons interact. In the course of doing so, it sheds bright light on a number of murky topics ranging from the possibility of all-things-considered moral conflicts to the mechanics of exclusionary reasons to the role of principles in moral theory. And even more excitingly, it poses sharp and difficult important new questions whose shape would not be visible if not for the clarity offered by the framework of the book." --Mark Schroeder, University of Southern California