Facing the Future: Agents and Choices in Our Indeterminist World

518 Pages·2001·26.43 MB·English

by  Nuel Belnap

Facing the Future
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FACING THE FUTURE
Agents and Choices in Our Indeterminist World
NUEL BELNAP
MICHAEL PERLOFF
MING XU
With Contributions by
Paul Bartha
Mitchell Green
John Horty
OXPORD
UNIVERSITY PRESS
2001
OXFORD
UNIVERSITY PRESS
Oxford New York
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Copyright © 2001 by Oxford University Press, Inc.
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All rights reserved No part of this publication may be reproduced,
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without the prior permission of Oxford University Press
Library of Congress Cataloging-in-Publication Data
Belnap, Nuel D , 1930-
Facing the future • agents and choices in our indeterminist world /
Nuel Belnap, Michael Perloff, Ming Xu, with contributions by Paul Bartha,
Mitchell Green, John Horty.
P cm
Includes bibliographical references and index.
ISBN 0-19-513878-3
1 Agent (Philosophy) 2. Choice (Psychology) 3 Free will and determinism
I Perloff, Michael II Xu, Ming III Title
B105 A35 2001
128'4—dc21 00-064995
9 8 7 6 5 4 3 21
Printed in the United States of America
on acid-free paper
Preface
This is a book about the causal structure of agency and action. It frames a
rigorous theory by using techniques and ideas from philosophical logic, philos-
ophy of language, and metaphysics with a small "m." This theory, which we
sometimes call "the theory of agents and choices in branching time," describes
agents as facing a future replete with real possibilities, some of which various
agents realize by making choices. It is central to our theory that choices and
the actions that they ground are radically indeterministic: Before an event of
choosing, there are multiple alternatives open to the agent. Furthermore, since
the choice is real, so must be the alternatives, and each alternative must be as
real as any other. All we can say before the moment of choice is that the agent
will make one of the open choices, leaving behind the unchosen alternatives.
After the choice, it is correct to say that they were once possible, but are no
longer possible. None of the possible choices is a mental or linguistic figment,
nor is any a mere ghost image of "the actual choice." Given that the possibil-
ities relevant for action are always possibilities for our future, the theory also
refrains from appealing to "possible worlds" other than the one and only world
that we all inhabit.
These ideas are in some part rooted in common sense. Without help, however,
common sense cannot seem to pull them together into a coherent whole. One of
our principal aims is to carry out that job by articulating them in a completely
intelligible exact theory. The resultant theory of agents and choices in branching
time pictures the causal structure of our world as made up of alternative courses
of events branching tree-like toward the future. Each branch point represents
a choice event or chance event. On the one hand, each continuation from a
branch point is individually possible; on the other hand, it is impossible that
more than one of these continuations should be realized. If that sounds obscure,
we agree: It is, we think, almost impossible to speak clearly and accurately about
indeterminism except in the framework of a rigorously fashioned theory such as
the one we propose.
The theory of agents and choices in branching time is of real but limited
interest without its application to understanding the language of action. We
propose a certain linguistic form, a "modal connective," as being unusually
helpful to anyone who wishes to think deeply about agents and their actions.1
1Our usage here is common but not universal. A connective is any grammatical construe-
vi Preface
The form is "a sees to it that Q," where a names an agent and Q holds the
place of a sentence; for example, we think of "Ahab sailed the seven seas" as
"Ahab saw to it that he sailed the seven seas." The form is so important to our
enterprise—all but three of our eighteen chapters are devoted to its study or
use—that we give it an abbreviation, "[a stit: Q]" with "stit" as an acronym
for "sees to it that." Stit theory explains the meaning of [a stit: Q] in the idiom
of philosophical logic. In doing so, stit theory invokes a certain melding of the
Prior-Thomason indeterministic semantics with Kaplan's indexical semantics.
The combined semantics make [a stit: Q] roughly equivalent to "a prior choice
by a guaranteed that Q."
The stit idea is many-sided. We explore its grammar, semantics, and proof
theory as logicians do. We delight in the fact that stit does not treat actions pri-
marily as "things" to be counted or named. We explore some of the linguistics
of stit (especially how and why its status as a modal connective lends itself to
usefully complicated constructions), we consider some applications to difficult
conceptual problems, and we argue the ability of stit to illuminate agency in a
variety of ways. We look at some ways in which stit might be modified or gen-
eralized. In all of this, however, we try never to forget the central constraining
thought: There is neither action nor agency nor doings without real choices,
choices that find their place not merely in the agent's mind, but within the
(indeterminist) causal order of our world. To see to it that Q, an agent must
make a real choice among objectively incompatible future alternatives.
When we say that an event may have many possible but incompatible out-
comes, we thereby come down on the side of "hard" indeterminism as against
determinism. There is no consensus on these ideas. Since the eighteenth cen-
tury became understandably awed by the success of Newtonian science, the
presumption of determinism has guided most of the philosophical and scientific
explorations of both agency and nature. Taking determinism to be delivered
by science as an unquestioned "fact," philosophers since Hume and Kant have
worked at developing "compatibilist" theories that hold agency, in the guise of
moral responsibility, to be compatible with what James called the block uni-
verse. Such theories have often taken possibilities as unreal: as arising from the
mind, or from social practices, or from language—for example from consistency
with the bits of language called "scientific laws." Our contrasting indeterminis-
tic presumption is eloquently expressed by the eminent paleontologist Stephen
Jay Gould.
I don't think that any deeper or more important principle pervades
nature, and lies at the heart of all historical sequences, than this cen-
tral but underappreciated notion of "contingency"—the great and
tion that maps one sentence (or several sentences) into another sentence. For example, when
you put sentences (i) "Ahab is captain" and (ii) "Ishmael is not captain" into the blanks of
" and ," the result is another sentence, (iii) "Ahab is captain and Ishmael is not captain."
That makes the "and" construction a connective. A truth functional connective is one like "
and ": If for example you know whether each of (i) and (ii) is true, then you automatically
know whether (iii) is true. A modal connective is defined negatively as being one that is not
truth functional.
Preface vii
liberating truth that tiny inputs, virtually invisible and risibly impo-
tent in appearance at the outset, can cause history to cascade down
any route in a vast array of entirely different pathways. (Gould 1999,
p. 30)
This book neither argues for indeterminism nor tries to pick holes in argu-
ments for compatibilism. Our project assumes the indeterminism of the causal
order in which agency is embedded, it assumes that actions are based on real
choices, and it assumes that choices are therefore not predetermined. Our goal
is not to persuade, but to make these ideas intelligible. Although numerous
philosophers share our general point of view, not many exact theories share these
assumptions and aims. Our strategy is to concentrate almost exclusively on the
objectively causal side of indeterminism and agency, which already presents
enough difficulties without bringing in noncausal concepts. We therefore lay
aside many deeply important aspects of agency and choice that involve inten-
tions, propositional attitudes, or other mental phenomena.
We look for ways in which applications of stit theory can engender a better
understanding of agency. Seven examples: (i) an analysis of refraining that clar-
ifies how it can be both a doing and a not-doing; (ii) an analysis of imperatives
that emphasizes their agentive content; (iii) an extended treatment of deontic
logic that insists that obligations and permissions (a) are directed to agents
capable of making choices, and (b) are embedded in the indeterministic causal
order of our world; (iv) fresh analyses of promising and of assertion, analyses
that argue the unwisdom of the doctrine that among all the objective possibili-
ties, a unique course of events constitutes the one and only "actual future"; (v)
an exploration of the causal side of the requirement on action that the agent
"could have done otherwise"; (vi) the causal structure of joint agency; and (vii)
a generalization of stit theory to strategies considered from a causal point of
view.
In sum: Holding the extra-mental and extra-linguistic status of incompatible
possibilities as given, and supposing that the future sometimes depends upon
an agent's choices among incompatible options, we offer a tense-modal theory
intended to describe some causal aspects of agency in our indeterministic world.
Guidance on reading this book. In the spirit of Carnap, each chapter
begins with some introductory remarks in order to permit easy skipping of
topics not of present interest to the reader. We append the following large-
scale structural notes as additional guidance. The book divides into six parts
of varying degrees of technicality, followed by an appendix. Each of these may
be characterized as follows.
Part I introduces stit theory. We intend the chapters in this part to be ac-
cessible to all those with an interest in our topic. Portions of chapter 2 and
chapter 5 do, however, involve willingness to put up with some elementary logi-
cal constructions, and chapter 2 offers a brief explanation of the theory of agents
and choices in branching time that underlies stit theory. In this part we intro-
duce key grammatical and semantic features of stit, including the distinction
viii Preface
of the deliberative stit from the achievement stit. Largely concentrating on the
achievement stit, the various chapters of part I suggest applications with the
help of many pictures, make comparisons with some other work on agency, and,
beginning with Anselm's work in 1100, give a little history of the modal logic of
agency. This part also contains applications of stit theory to imperatives and
to promising.
Part II supplies precisely and in detail the nuts and bolts—or, more aptly,
roots and branches—of the theoretical structure that supports our account of
agents, actions, and our indeterminist world. The three chapters of this part
are foundational in character, and involve substantially more rigor, though not
much more mathematics. They stress conceptual analysis rather than theorem-
proving. This part more than any other focuses on the problems faced by
any indeterministic theory. Here we argue against the beguiling but harmful
doctrine of "the actual future," which says that among the many courses of
events that might come to pass, there now exists a privileged such course that
will actually do so. This foundational part examines, postulate by postulate,
the theory of agents and choices in branching time, and explains in detail the
semantic subtleties required of a language spoken in an indeterminist world.
Part III offers two applications of the achievement stit: One chapter aims to
illuminate the dark idea of "could have done otherwise," and another considers
the causal aspects of joint agency. These chapters are a little more technical.
Part IV is of the same level of technicality as part III: It offers applications
of the deliberative stit, chiefly to help in elaborating such deontic concepts as
obligation and permission, which, we believe, are in much need of a theory of
agency.
Part V uses the already-established theoretical structure of agents and choices
in branching time in order to develop an austere (causal, not normative) account
of strategies as a kind of generalization of stit. One chapter in this part connects
our theory of strategies to Thomason's deontic kinematics. Part V proves a
theorem or two, though much of it is, again, conceptual analysis.
Part VI provides the technical backbone of stit theory, including proofs of de-
cidability, soundness, and completeness. The chapters of this part are required
reading for those who wish to investigate or develop the logical and mathemat-
ical properties of theories of agency similar to ours.
The appendix gathers, for easy reference, most of the various theses, struc-
tures, postulates, definitions, semantic ideas, and systems that are introduced
elsewhere and are employed throughout the book. We use boldface to refer to
certain of these items: Look in the appendix for its sections §l-§9, for stit the-
ses Thesis 1-Thesis 6, for postulates Post. 1-Post. 10, for definitions Def.
1-Def. 20, and for axiomatic concepts Ax. Conc. 1-Ax. Conc. 3.
Although in each section of this book we feel free to refer to any other section,
it may be useful to indicate the following dependency-structure among the vari-
ous parts. Parts I (introduction to stit), II (foundations of indeterminism), and
VI (proofs and models) are almost entirely independent. The reader's primary
interests may therefore be allowed to determine with which of parts I, II, or VI
it is best to begin. Part III (applications of the achievement stit) and part IV
Preface ix
(applications of the deliberative stit) are mutually independent, whereas each
presupposes familiarity with part I. Part V (strategies) requires chapter 2 of
part I as minimum background.