DeYoung-000.

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Aquinas’ s
Ethics
Metaphysical Foundations,
Moral Theory, and Theological Context

Rebecca Konyndyk DeYoung,

Colleen McCluskey, and Christina Van Dyke

University of Notre Dame Press

Notre Dame, Indiana

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Copyright © 2009 by University of Notre Dame

Notre Dame, Indiana 46556
www.undpress.nd.edu
All Rights Reserved

Manufactured in the United States of America

Library of Congress Cataloging-in-Publication Data

DeYoung, Rebecca Konyndyk.

Aquinas’s ethics : metaphysical foundations, moral theory, and
theological context / Rebecca Konyndyk DeYoung, Colleen McCluskey,
and Christina Van Dyke.
p. cm.
Includes bibliographical references and index.
isbn-13: 978-0-268-02601-1 (pbk. : alk. paper)
isbn-10: 0-268-02601-7 (pbk. : alk. paper)
1. Thomas, Aquinas, Saint, 1225?–1274. 2. Ethics, Medieval.
I. McCluskey, Colleen, 1957 – II. Dyke, Christina van, 1972 –
III. Title.
b765.t54d475 2009
241'.042092 — dc22
2009006989

∞ The paper in this book meets the guidelines for permanence and
durability of the Committee on Production Guidelines for Book Longevity
of the Council on Library Resources.

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Introduction

S t. Thomas Aquinas (1224/25 –1274) is a towering figure in the

history of philosophy; few scholars can rival either the breadth or the
depth of his intellectual pursuits. Above and beyond his independent
works (including, most famously, the Summa theologiae and the Summa
contra gentiles), Aquinas also wrote extensive commentaries on most of
Aristotle’s treatises and on numerous books of the Bible. In addition, he
participated actively in the intellectual debates of his day, writing strongly
against philosophical and theological doctrines that he thought were er-
roneous. His scholarly accomplishments have been renowned in philo-
sophical and theological circles for over 750 years.
Aquinas’s reputation for brilliance is somewhat dulled, however, by
his reputation for tedious prose and meticulous attention to detail. In gen-
eral, his style of careful argumentation, set in the question-and-answer
format that epitomizes high medieval scholarship, is often caricatured
as concerned primarily with abstract questions, such as how many angels
can dance on the head of a pin.1 Yet, as we will argue in this book, to think
of Aquinas’s philosophical project— and, in particular, his ethics— as ir-
relevant to modern life is to miss its central point. When one takes the
time to fit the different pieces of his thought together, one is rewarded
with a richly integrated picture of the genuinely happy human life.

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2 Aquinas’s Ethics

Why is it, after all, that two people can live on the same street, work
at the same job, and yet one person experiences constant frustration and
anxiety in his life while the other flourishes? Is it better to become a ma-
rine biologist or a day-care worker? Can anyone justify becoming a pro-
fessional musician when people are starving throughout the world? How
are we to think about the ultimate purpose of our lives — how are we,
for example, to balance personal fulfillment with the demands of living
in community?
Aquinas’s account of human nature and human flourishing turns
out to provide a meaningful framework in which to answer pressing life
questions. While recognizing that each of us possesses unique talents and
shortcomings, he describes a general picture of the flourishing life that
proves as provocative, challenging, and attractive today as it first did over
seven hundred years ago. Our central goal in this book is to present this
rich picture to readers who lack the time or technical expertise to under-
take the project themselves.
Aquinas develops his account of the genuinely happy life within a
complex metaphysical and theological framework; thus, a large part of
our task will be to examine his understanding of what human beings are
and how and why they act. With this foundation in place, we’ll be able
to properly appreciate his conception of the good life human beings are
meant to live.
Aquinas’s own life underscores his belief that scholarly pursuits
can— and perhaps should— have practical as well as abstract or contem-
plative results. When his politically-minded family pressured him to join
the highly respected and well-established Benedictine monastic order,
Aquinas did not object to the idea of a religious career in and of itself.
Instead of choosing the Benedictines, however, he insisted on joining
the recently formed Dominican order, a religious order with considerably
less prestige and a radical social mission. Founded in 1217 by St. Dominic,
a leader with a strong desire to revitalize the church’s mission and to
rescue it from religious apathy and power-hungry clergy, the Domini-
can order dedicated itself to a life that combined quiet prayer and con-
templation with active Christian service. Like the Franciscans (another
recently founded religious order), the Dominicans served as itinerant
teachers and preachers, explicitly pursuing intellectual formation for the

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Introduction 3

sake of spiritual formation. By joining this order, Aquinas was consciously

choosing to integrate the work of his intellectual and spiritual contem-
plation with an active life of preaching and teaching.
Contemporary readers can see this integration in Aquinas’s developed
account of human virtue. Instead of focusing purely on a theoretical un-
derstanding of the nature of a good moral character, Aquinas also pro-
vides practical instruction for living well. When he discusses virtues and
vices in the Summa theologiae, for example, he addresses not just abstract
questions, such as how we should define virtue, but also practical issues,
such as how to show gratitude toward someone who does us a favor we
are too poor to repay. This dual concern shows up repeatedly in his ethi-
cal works and underscores his commitment to putting belief into action.

Aquinas’s Connection to Aristotle

The strategy of Aquinas’s ethical theory closely mirrors Aristotle’s ap-

proach in the Nicomachean Ethics. Aristotle (384–322 b.c.), whose work
profoundly influenced Aquinas’s thought, has an explicitly practical aim
in his Ethics: he wants to explain to people what the true nature of hap-
piness is, so that they can work toward actually living the happy life. Ac-
cording to both Aristotle and Aquinas, every human being desires her or
his own happiness, and all human beings do what they do for the sake of
becoming happy. Since both see happiness as the end goal of human life
and the fulfillment of human nature, they approach ethics as the study
of how human beings can best fulfill their nature and obtain happiness.
Ethics thus has a practical as well as a theoretical goal. Its dual purpose
naturally affects how we should undertake its study. In the same way that
the point of going to the doctor with a persistent migraine is not simply
to learn more about the migraine but to actively rid oneself of the pain,
so the point of reading ethics and thinking about how we should live our
lives is to actually live our lives differently— to live them better.
Aquinas and Aristotle agree both that the study of ethics should have
a practical goal and that the life of happiness is the end goal for human
beings. Because they begin with differing metaphysical and theological
commitments, however, they diverge when they approach the nature of

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4 Aquinas’s Ethics

this ultimate end. Aristotle stresses our status as rational animals and de-
scribes the happy life rather broadly as “the life of activity expressing rea-
son well.”2 Aquinas, on the other hand, emphasizes our status as beings
created by God; the point of the ethical life for Aquinas is, correspond-
ingly, not just a life of flourishing rationality but, more specifically, a life
of intimate union with God. Thus, while Aristotle is highly interested
in moral education and character formation, Aquinas sees the deeper
purpose of moral education and character formation as preparing us
for union with God. Aristotle believes that having the right moral char-
acter is necessary for the flourishing human life, and that the right use
of reason will show us what counts as the right sort of moral character.
Aquinas believes that we are created in God’s image, and that we flourish
most when our likeness is closest to that image — that is, when we most
closely resemble God in the ways appropriate to human beings.
As we demonstrate throughout this book, Aquinas’s central project
in his ethics is grounded in these metaphysical and theological beliefs.
Indeed, one of the most striking features of Aquinas’s scholarship is its
conscious synthesis of Aristotelian philosophy with his Christian beliefs.
He is sometimes said to “baptize Aristotle,” but what Aquinas does in his
independent works (such as Summa theologiae) goes much deeper than
sprinkling a few Christian sentiments over a generally pagan system;
rather, his theological commitments permeate his philosophical system.
By keeping Aquinas’s Christian beliefs firmly in mind, we will better un-
derstand three central components of his philosophy: the metaphysics of
his account of human nature, the theory of action he develops on the basis
of that metaphysics, and his ethical theory. With this approach, readers
can appreciate the full richness and value of Aquinas’s thought.
To demonstrate why we believe a proper understanding of Aquinas’s
philosophy requires its being seen as part of this larger picture, it is useful
to turn to Summa theologiae IaIIae, questions 1– 5. These five questions,
commonly referred to as the treatise on happiness, are a prime example
of how Aquinas actively integrates his theological beliefs with an Aris-
totelian metaphysical and ethical system. Over the course of these ques-
tions, Aquinas addresses the opening book of Aristotle’s Nicomachean
Ethics, a book that culminates with Aristotle’s famous function argument
for human happiness. By examining briefly both the original function ar-

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Introduction 5

gument and Aquinas’s treatment of it, we can see how Aquinas simulta-
neously accepts and transforms Aristotelian claims within a deeply Chris-
tian context.
In the Nicomachean Ethics 1.7, Aristotle makes a connection between
something’s nature and its function. He claims that everything has a func-
tion or a characteristic activity. The function of a knife, for example, is
“to cut.” The fact that a knife’s function is cutting is hardly accidental to
its being a knife; rather, a thing’s characteristic activity relates directly
to its nature. Broadly speaking, what a thing is explains what that thing
properly does. So, for example, the fact that a knife’s essence just is “cut-
ting tool” accounts for the fact that the function of a knife is “to cut.”
Human beings, too, have a function, one that is best understood by
reference to their nature. According to Aristotle, humans are rational ani-
mals. They are animals insofar as they are living, breathing physical crea-
tures, but they differ from all other animals in their ability to cognize —
that is, in their rational abilities. This understanding of human nature
gives us the key to identifying the human function: since, by nature, an
animal lives a life of activity (perceiving with its senses, seeking food,
shelter, etc.) and since, by nature, a rational being engages in intellectual
cognition, the function of a rational animal must be “a life of activity ex-
pressing reason.” Thus, the characteristic activity of a human being—
the activity that fully captures what it is to be human — is not just ac-
tivity common to other animals but activity that specifically employs our
rational capacities.
Although grounded in Aristotle’s metaphysical beliefs, this descrip-
tion of the human function also has deep implications for his ethics. Aris-
totle holds that a thing’s virtue — its excellence — necessarily involves
that thing’s performing its function well. (Aristotle’s claim here is a meta-
physical one: to say a knife is excellent or virtuous insofar as it cuts well
is to say that it is a good knife, not that it is a morally good knife.)3 A thing
is excellent precisely when it does a good job in carrying out its charac-
teristic activity. A knife’s function is to cut, and so its virtue or excellence
consists in its actively cutting well. In the same way, since the human
function involves a life of activity expressing reason, human virtue —
human excellence — consists in performing that function well. (In this
connection, it is important to remember that reasoning itself counts as

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6 Aquinas’s Ethics

an action.) Thus, our excellence consists not merely in employing our

rational capacities but in employing them well.
Aristotle goes on in the Ethics to link virtue with human happiness.
The highest good, he claims, is happiness. Moreover, the good of a human
being is his or her happiness, and what’s good for a human being is to
be good at the human function. This might at first seem puzzling, but if
one’s function follows directly from one’s nature, then performing that
function actualizes that nature; the better you are at your function, the
more you fulfill your nature. Thus, there does seem to be a clear sense
in which being good at the human function— living a life of activity ex-
pressing reason— is good for you. When you are good at it, you exist fully
as the very sort of thing you are. You actualize all of your natural abilities
in the best possible way. This radical fulfillment of your nature is happi-
ness, and so, Aristotle concludes, happiness for human beings is itself the
life of activity expressing reason well; or, as he also puts it, happiness is
the life of activity expressing virtue.4
Aquinas fundamentally agrees with Aristotle both that human be-
ings are rational animals and that the human function can be properly un-
derstood as living the life of activity expressing reason. He also agrees that
human excellence consists in performing that function well. He holds,
however, that these claims need to be further understood in the context
of our status as created beings. In the prologue to his treatise on hap-
piness, Aquinas states that human beings are created in the image of
God. This fact is essential to understanding their nature, he claims, since
“human beings are said to be made in the image of God, where ‘image’
signifies ‘intellectual being who possesses both free choice and power over
its actions.’” What it means for us to be created in God’s image, accord-
ing to Aquinas, is, first and foremost, that we possess intellect, will, and
the resulting ability to act on our own power. This link to the Creator fur-
ther explains why our function involves both reasoning well and acting
on the basis of that reasoning. We have intellects and wills, capacities that
allow us to discover what our powers to act are intended for and how we
are meant to act. In short, we are teleological beings, created by God with
a particular function and for a particular purpose.
Although Aquinas agrees with Aristotle’s basic metaphysical and
ethical claims concerning the human function, excellence, and happiness,

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Introduction 7

then, he goes beyond Aristotle in arguing that what it means for us to live
“the life of activity expressing reason well” needs to be understood in the
context of our relationship to the Creator. In particular, Aquinas claims
that our excellence consists in the activity of knowing and loving God.
Thus, when Aristotle identifies happiness as the highest good and
our ultimate end, Aquinas concurs — and then he identifies that highest
good with God. Again, when Aristotle argues that the activity of hap-
piness consists in the fullest expression of our rational powers, Aquinas
agrees — and then he explains that the fullest expression of our rational
powers involves both the cognition of our ultimate end and the proper
response to that knowledge. For him, the activity of human happiness
consists both in our cognition of God, our ultimate end, and in our ap-
propriate reaction to that ultimate end— namely, love. The activity of
human happiness thus maximizes our nature as created rational beings
by putting our distinctively human capacities to their best possible use.
Since human beings are unique among animals by being created in God’s
image, by possessing intellect and will, perfect human happiness involves
knowing God through our intellects and loving God with our wills.
This brief glance at Aquinas’s interpretation of the function argu-
ment demonstrates both how his ethical system depends on his theories of
human nature and human actions and how Aquinas freely directs Aris-
totle’s basic philosophical precepts toward an explicitly Christian end. It
also gives us a basic idea of the flourishing human life as he understands it.

Happiness as the End of Human Nature

and Human Actions

Human beings are notorious for failing to flourish, however. In fact,

even if we had enormous amounts of time, energy, and money to devote
to satisfying our wants and needs, few of us would count as happy on ei-
ther Aristotle’s or Aquinas’s standard. Part of the problem, as both schol-
ars would be quick to observe, is our ignorance of what our end actually
is. There is much more to the story of human misery, however, and an
integrated reading of Aquinas’s thought on human nature and action
can provide a surprisingly cogent explanation for our unhappiness. In

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8 Aquinas’s Ethics

particular, his account of our actions as the end-product of a complex se-

ries of interactions between the intellect and the will can help us see more
clearly both how we often fall short of fulfilling our own nature and the
consequences this has for our moral life. Just as importantly, it can help
us understand how Aquinas believes we can become right again—with
ourselves, with others, and with God.

T o present our reading of Aquinas’s ethics within its original philosophical

and theological context, we have divided this book into three main parts:
one addressing his metaphysics, one examining his action theory, and the
last showing how Aquinas believes virtue, law, and grace fit together in
the flourishing human life of happiness.5 As we will see, to fully compre-
hend his ethical theory we need to understand why Aquinas character-
izes properly human actions as interactions between intellect and will. To
appreciate his descriptions of these interactions, however, we must begin
with his account of the nature of human beings as rational animals, cre-
ated in the image of God.
For this reason the first chapter lays out the metaphysical founda-
tions of Aquinas’s account of human nature, focusing on the particular
niche that human beings occupy in the continuum between pure actu-
ality (God) and pure potentiality (prime matter). In the second chapter we
move to a closer discussion of human nature. We examine how Aquinas’s
claims that we are composites of matter and form and that we are physi-
cal bodies with immaterial intellects presents a picture of human nature
in which our physicality is essential to us — in which human beings are
living bodies. Finally, in chapter 3 we turn to Aquinas’s account of human
capacities, since what human beings are relates closely to what they can
do. The most important capacities for our purposes are, of course, intel-
lect and will, and so part 1 of this book concludes with a discussion of
those two capacities.
In part 2 (chapters 4– 6) we build on this picture of intellect and will
by looking at Aquinas’s complex and interesting account of human ac-
tions. In chapter 4 we consider why we perform any actions at all— that
is, we examine the ultimate goal or purpose of our actions. Next we look
at what Aquinas thinks we are doing when we perform an action. We

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Introduction 9

can think of this as the mechanics of action: how Aquinas accounts for
the fact that human actions are produced in the first place. Understand-
ing the mechanics of action enables us to appreciate what it is to perform
good actions and how action goes wrong, which is the focus of chapter 5.
Finally, in chapter 6, we consider the freedom of human action. Freedom
is an important condition for moral appraisal; ordinarily we do not think
that individuals should be held accountable for their actions if it turns
out that they did not perform those actions freely. Human freedom also
generates certain tensions with other commitments within Aquinas’s
ethics — the efficacy of grace, for example. Thus, both chapters 5 and 6
set the stage for understanding Aquinas’s ethical theory, which is the
focus of part 3.
In this last part (chapters 7– 9) we examine three integrated elements
of Aquinas’s moral thought—virtue, law, and grace — in order to un-
derstand his conception of human flourishing. First, we address the way
virtues perfect the human capacities that are essential to flourishing and
show how perfection in virtue unites us with God. Our union with God,
for Aquinas, is a relationship modeled on Aristotelian friendship, a rela-
tionship based on goodness of character and a shared love of the good.
This love, which Aquinas calls charity (caritas), is an activity specific to
human beings and other persons (such as God and the angels), in that
it requires intellect and will.6 Second, we examine the way that law and
grace, rather than standing apart from virtue, are an integral part of this
picture of human moral formation. Law and grace show us how and why
divine agency is necessary for us to reach our ultimate end, but in a way
that leaves room for our freedom. Finally, through a study of a particu-
lar virtue and vice, we demonstrate how Aquinas’s theological commit-
ments and, in particular, the centrality of the theological virtue of charity
shape both the content and purpose of his ethical work.
It is our hope that by the end of this book, readers will understand
Aquinas’s ethical theory within its original context; furthermore, we hope
that our readers will be drawn to share our appreciation for both the use-
fulness and the appeal of Aquinas’s account of the good life.
One further introductory remark is in order: given Aquinas’s stat-
ure in the history of philosophy and his thorough treatment of topics of
perennial interest to professionals as well as nonprofessionals in both

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10 Aquinas’s Ethics

philosophy and theology, it should come as no surprise that the exami-

nation of the three central areas of his work addressed in this book con-
stitutes an industry in itself. While no one can expect to do full justice
to Aquinas’s thought without addressing this rich and complex second-
ary literature, we have made a deliberate decision not to engage that lit-
erature directly here. Each of us is conversant with the appropriate lit-
erature, and it has influenced our own interpretations of Aquinas’s texts
in significant ways —ways we have explicitly addressed elsewhere. For
the purposes of this work, however, we have chosen to focus on our
own explications of Aquinas’s views (especially those found in his most
famous text, Summa theologiae) in order to give the reader an appreci-
ation for the breadth, depth, internal cohesiveness, and ultimate practi-
cality of Aquinas’s account. We have avoided the kinds of distractions
that would naturally arise in a project that strove both to provide a sub-
stantive interpretation of Aquinas’s ethical theory— including its com-
plex foundations — and to address the many controversial issues that
occur in the secondary literature. Of course, sophisticated readers will re-
alize that our elucidation is not the only alternative; we encourage these
readers to pursue further study both of Aquinas’s own texts and of the
voluminous secondary literature. In fact, if this book leads to such study,
we will consider that an equally welcome result of our work here.
Given this approach, we expect that this volume will prove especially
useful to those readers who are encountering Aquinas for the first (or
perhaps the second) time. Nevertheless, we also hope that experts in this
area will find our book interesting and relevant for their own purposes.
While our approach leaves open exactly how we respond to interpretive
debates in the wider literature, we trust that our offering provides food
for thought even for those thoroughly conversant with Aquinas’s views.

© 2009 University of Notre Dame Press