Thagard offers a detailed framework for understanding how
scientists explain disease and how new explanations gain acceptance. The book’s focus is on medical research, not
clinical practice. This book is not for
the reader looking for a practical account of clinical diagnosis and
treatment. But for the reader looking
for a thorough and rigorously analytic account of scientific explanation of disease,
Thagard’s book is an important contribution to the philosophy of medicine
literature.

How Scientists Explain Disease is
divided into four main sections. The
first begins with scientific explanation, generally, and then disease
explanation, specifically. Thagard
offers an overview of various explanations of the development of scientific
knowledge coming from a range of fields including philosophy, sociology, and
psychology. Here we get the beginning
of his argument that the development of scientific knowledge relies on both
cognitive and social explanations.

The
Integrated Cognitive-Social Explanation Schema is Thagard’s model for
understanding scientific explanation and the development of scientific
knowledge. Explanation schemas consist
of a target and a pattern. The target
identifies the question and the pattern provides an answer. In this book the key explanation target is
“Why did a group of scientists adopt
a particular set of beliefs?” The explanatory pattern includes the
scientists’ own mental representations, previous beliefs, and interests, as
well as their social connections and power relations. When the social context is applied to their mental
representations and previous beliefs, a new set of beliefs is adopted. The bulk of the book fills out an argument
for this explanation schema.

The
explanations produced by medical researchers resemble this schema. In explaining disease, the target question
becomes “Why does a patient get a cancer?” or “Why does a patient get a disease with associated symptoms?” The terms in boldface are replaced with
specific details. Thagard argues that
medical knowledge comes from “the broad applicability of an organized system of
explanation schemas” (20).

The
second section of the book uses the bacterial theory of peptic ulcers as a case
study to illustrate the acceptance of a new theory of disease. He furthers his argument for the Integrated
Cognitive-Social Explanation Schema by showing that the acceptance of the
bacterial theory required cognitive, social, and physical processes. Although Thagard argues that social
processes play an important role in the advancement of medical knowledge, he is
a realist, which means that he thinks that diseases and their causes are real
things out in the world apart from us; they are not social constructions. When scientists explain a disease, such as
peptic ulcers, they identify real
causes and evidence that support the claim that bacteria cause ulcers.

The third
and fourth sections focus on the cognitive and social processes that make up an
explanation schema. Cognitive
mechanisms include “causality, analogy, and conceptual change” (117). Disease explanations are “instantiations of
complex causal networks” (117); thus it is important to understand how
scientists identify causes and produce new scientific theories. In one particularly interesting chapter
Thagard uses the examples of scurvy, mad cow disease, AIDS, and chronic fatigue
syndrome to illustrate the difficulty of understanding a disease. “Understanding a disease requires
characterizing its symptoms, specifying possible causes, determining actual
causes experimentally, and elaborating the mechanism by which the cause
produces the disease” (133). These each
involve cognitive processes, but the process is often highly complex and major
conceptual changes are often required. 
For example, chronic fatigue syndrome is controversial because there is
a wide range of symptoms and because scientists have not been able to identify
causal agents.

The
chapters on social processes both describe the processes involved in the
development of scientific knowledge and assess them. Thagard describes the role of collaboration in science and argues
for its importance. Social processes
range from the use of consensus conferences in medicine to the use of the
Internet by researchers. Science is a
social process and Thagard argues that social processes further scientific
knowledge in significant ways.

Thagard
concludes by offering an analogy for understanding the development of
scientific knowledge. The analogy is
with distributed artificial intelligence which studies how a network of
computers is able to collectively accomplish tasks beyond the capability of any
one computer (224). Scientific
communities are like networks of computers. 
Collectively scientists are able to accomplish beyond the ability of any
one scientific mind. Thagard’s argument
is anti-reductionist; it is impossible to understand social processes purely in
individual terms and it is also impossible to understand individual
psychological processes completely in social terms. His argument lies in the middle of two extremes: on one end is
the view that science is completely a social construct; on the other end is the
view that science is logic.

In
the book’s preface Thagard claims that the book is intended for two audiences:
those with a general interest in the study and explanation of particular
diseases and second, for philosophers, historians, sociologists, and
psychologists. In my opinion, the book
is probably of most interest to the latter group. Some descriptions, for example his account of causal reasoning,
might be too technical for a lay reader. 
However, understanding such details is not integral to understanding the
general thrust of Thagard’s arguments and he nicely leads the reader through by
offering succinct summaries along the way.

© 2002 Susan Parry

Susan Parry is a
Ph.D. candidate in the Department of Philosophy at the University of Minnesota
and is a Research Assistant at the University’s Center for Bioethics. She is writing a dissertation on ways in
which patient desires shape the practice of medicine. Her general interests are in bioethics and philosophy of science.

Categories: Philosophical