Causality, Probability, and Medicine

Donald Gillies

• Publisher: Routledge
• Year: 2018
• eBook ISBN: 9781317564287
• Topic: Philosophy
• Subtopic: Philosophy History & Theory

Why is understanding causation so important in philosophy and the sciences? Should causation be defined in terms of probability? Whilst causation plays a major role in theories and concepts of medicine, little attempt has been made to connect causation and probability with medicine itself.

Causality, Probability, and Medicine is one of the first books to apply philosophical reasoning about causality to important topics and debates in medicine. Donald Gillies provides a thorough introduction to and assessment of competing theories of causality in philosophy, including action-related theories, causality and mechanisms, and causality and probability. Throughout the book he applies them to important discoveries and theories within medicine, such as germ theory; tuberculosis and cholera; smoking and heart disease; the first ever randomized controlled trial designed to test the treatment of tuberculosis; the growing area of philosophy of evidence-based medicine; and philosophy of epidemiology.

This book will be of great interest to students and researchers in philosophy of science and philosophy of medicine, as well as those working in medicine, nursing and related health disciplines where a working knowledge of causality and probability is required.

PART I
Causality and action

1

An action-related theory of causality

In the introduction I have described an important group of philosophical ­theories of causality, which were called AIM theories, where AIM means Action, Intervention, Manipulation. In this chapter I will discuss the historical development of AIM theories, and put forward a particular theory of this type, which will be called “an action-related theory of causality”. Then in the next chapter, I will give a general discussion of AIM theories of causality, showing how they attempt to overcome the difficulties in this approach, and what are the points in their favour. This discussion will give a comparison of the action-related theory advocated in this book with other contemporary versions of AIM theories of causality.

In the introduction I mentioned some ancestors of the AIM approach to causality, most notably Bacon. However, AIM theories of causality really only begin in the late 1920s and 1930s. Perhaps the first sketch of an AIM theory of causality is to be found in a paper by Frank Ramsey, ‘General Propositions and Causality’, which was written in 1929, and published after his death in 1931. This sketch consists of only three sentences which run as follows (Ramsey, 1931, p. 250) ¹ :

Again from the situation when we are deliberating seems to me to arise the general difference of cause and effect. We are then engaged not on disinterested knowledge or classification (to which this difference is utterly foreign), but on tracing the different consequences of our possible actions, which we naturally do in sequence forward in time, proceeding from cause to effect not from effect to cause. We can produce A or A’ which produces B or B’ which etc. … ; the probabilities of A, B are mutually dependent, but we come to A first from our present volition.

Here Ramsey argues that “the general difference of cause and effect” (in say “A causes B”) arises not from “disinterested knowledge” but from a consideration of “our possible actions”. So we can produce A which produces B. He contrasts the situation with probability by saying that “the probabilities of A, B are mutually dependent”. What Ramsey seems to mean here is that if A is probabilistically dependent on B, then B is probabilistically dependent on A, i.e. the relation is symmetric. By contrast, if A causes B, B does not in general cause A. This is because “we come to A first from our present volition”, which is to say that we use A to produce B, but not vice versa. As can be seen, this remarkable passage anticipates not only AIM theories of causality, but also the Humphreys paradox, which was described in the introduction. However, the passage is so short and cryptic that it must surely be described as a precursor rather than an exposition of these ideas.

The first to develop a detailed version of an AIM theory of causality in the 20th century were Collingwood, in a 1938 paper, and subsequent book (1940), and Dingler in his 1938 book. ² The AIM approach to causality was then espoused and developed by Gasking (1955), and von Wright in his 1973 paper and 1974 book.

More recently, there have been a number of developments of AIM theories of causality by philosophers of science. Menzies and Price have developed one of these theories (see Price [1992] and Menzies and Price [1993]). They refer to their theory as an agency theory of causality. Woodward (2003) has developed a theory which he calls: “a manipulationist or interventionist account of … causation” (p. v). I refer to my own version (Gillies 2005a) as an action-related theory of causality. Pearl’s 2000 book should also be mentioned here. Pearl is not committed exclusively to an AIM account of causality, and introduces other conceptions of causality into his scheme. However, intervention still plays an important role for him. He introduces the variable X₃ which stands for a sprinkler which can be on or off (2000, p. 23). He urges the reader: “Note the difference between the action do(X₃ = On) and the observation X₃ = On”. Later in the book, Pearl introduces a do-calculus, which is a mathematical way of representing interventions. AIM theories of causality are thus one of the leading trends in contemporary philosophy of causality. In this book, I will naturally follow my own AIM theory, which differs from some of the others. It is, however, perhaps the closest to Collingwood’s original version, and I will expound it by first stating Collingwood’s theory and then explaining how I think this needs to be changed and developed.

Before coming to Collingwood, however, I want to discuss briefly one famous paper on causality, even though this does not present, or even mention, an action, intervention, manipulation approach. The paper in question is Russell’s 1913 ‘On the Notion of Cause’, which was his presidential address to the Aristotelian Society in November 1912. This paper has a particular interest for me since I believed its conclusions for many years, and even though I now reject Russell’s overall position, I still think that some of his ideas are valid, and will attempt to incorporate these ideas into my action-related theory of causality. Moreover, Russell’s 1913 paper on causality was, as we shall see, very important also for Collingwood.

1.1 Russell’s critique of the notion of cause

Russell begins his paper in a dramatic fashion by claiming the word ‘cause’ should be altogether banished from philosophy (1913, p. 173):

In the following paper I wish, first, to maintain that the word ‘cause’ is so inextricably bound up with misleading associations as to make its complete extrusion from the philosophical vocabulary desirable; …

Russell’s principal reason for this recommendation is that the word ‘cause’ has already disappeared from the advanced sciences. As he says:

All philosophers, of every school, imagine that causation is one of the fundamental axioms or postulates of science, yet, oddly enough, in advanced sciences such as gravitational astronomy, the word ‘cause’ never occurs.

Russell, writing just before the First World War, concludes that causality, like the British monarchy, is something no longer appropriate in the modern age. With his customary wit, he puts the point as follows (1913, p. 173):

The law of causality, I believe, like much that passes muster among philosophers, is a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm.

In these quotations Russell has perhaps rather exaggerated his own position in the interest of some striking turns of phrase. If we read on, we discover that he does after all allow a weak notion of causality. However, he claims that this notion of causality is useful only in everyday life and the infancy of science. His main thesis, therefore, is that the concept of cause disappears from science as it advances.

Regarding the weak notion of causality which he in fact allows, Russell gives an analysis similar to a Humean “constant conjunction” account, except that Russell claims that the sequences are of frequent rather than absolutely constant conjunction, and that they yield no more than probability (1913, p. 185):

the sequence, in any hitherto unobserved instance, is no more than probable, whereas the relation of cause and effect was supposed to be necessary. … Thus in our present sense, A may be the cause of B even if there actually are cases where B does not follow A. Striking a match will be the cause of its igniting, in spite of the fact that some matches are damp and fail to ignite.

Thus causal laws for Russell are laws of probable sequence. He points out one curious consequence of this neo-empiricist or neo-Humean account, namely that it turns out to be correct to say that night causes day (1913, p. 185). Intuitively however the statement that night causes day does not seem to be true.

In terms of the analysis of causal laws as laws of probable sequence, Russell is in a position to state his main thesis which he does as follows (1913, p. 186):

such laws of probable sequence, though useful in daily life and in the infancy of science, tend to be displaced by quite different laws as soon as a science is successful. The law of gravitation will illustrate what occurs in any advanced science. In the motions of mutually gravitating bodies, there is nothing that can be called a cause and nothing than can be called an effect; there is merely a formula. Certain differential equations can be found, which hold at every instant for every particle of the system, and which, given the configuration and velocities at one instant, or the configurations at two instants, render the configuration at any other earlier or later instant theoretically calculable. That is to say, the configuration at any instant is a function of that instant and the configurations at two given instants. This statement holds throughout physics, and not only in the special case of gravitation. But there is nothing that could be properly called ‘cause’ and nothing that could be properly called ‘effect’ in such a system.

Russell’s position depends on distinguishing between different types of scientific law. Causal laws are those of the form: “A causes B”. However, there are other types of scientific law. Russell mentions functional laws relating variables, and laws expressed by differential equations. He could have added probabilistic or statistical laws, such as the law that radioactive emissions follow a Poisson distribution. Russell’s thesis is that causal laws are useful only in daily life and in the infancy of a science, and are not to be found in an advanced science.

I believed this thesis for many years, and I still think it is correct for theoretical physics. However, Jon Williamson persuaded me that it cannot be true for all advanced sciences, since it is plainly false for medicine. Considerations of causality arise at every step in medicine. Consider, for example, a doctor who carries out a medical diagnosis is attempting to ascertain the cause of a patient’s symptoms. If the patient suffers from pains in the chest, it is most important to know whether these are caused by lung cancer, angina, a bacterial infection of the bronchi, or something else altogether. The treatment given will be quite different for different causes. We see from this that the notion of cause and causal laws play a crucial role in medical practice.

The same applies to medical research, as can be illustrated by one of Pasteur’s famous medical discoveries (cf. Debré , 1994, pp. 330–40). In June 1879, Pasteur collected pus from the boil of one of his assistants, and discovered that it contained a bacterium which was later named staphylococcus. In February 1880 Pasteur took pus samples from deep in the bone of a little girl aged 12 who was being operated on for the bone disease osteomyelitis. He discovered that the pus contained a bacterium of the same type. This led him to conclude that boils and osteomyelitis are both caused by the same bacterium. This was a very significant discovery since it showed that a serious disease located deep in the tissues had the same cause as a superficial and generally slight illness. The result eliminated the difference between internal and external pathology. Note that this most impressive discovery was the discovery of a causal law.

Discoveries in medicine are used for either the prevention or the cure of diseases. In the case of staphylococcal infections, preventative measures were relatively easy. It was a matter of preventing the pathogenic bacterium entering the body through greater care about hygiene and antisepsis. The discovery of a cure proved much harder. It required finding a substance (an antibiotic) which would kill staphylococci in a patient’s body without harming the patients. Fleming discovered penicillin in 1928, but it required a lot of development work both by him, and later by the Oxford team of Florey, Chain, and others before penicillin could become an effective antibiotic. (For details see Macfarlane, 1984, especially pp. 165–186.) In fact, it was not until May 1941 that the first patient was cured of a staphylococcal infection (a four-inch carbuncle on the back) using penicillin. Hence 62 years elapsed between the discovery of the cause of a group of illnesses and the development of a successful cure. However, it is worth noting that the discovery of the cause was a precondition for developing a cure.

Returning now to Russell, we can see that medicine completely refutes his claim that causal laws belong only to the infancy of science. Medicine has been highly successful and produced cures which would have been regarded as miraculous in a former age. Thus medicine has every claim to be an advanced science, and yet makes essential use of the notion of cause and of causal laws. Russell, however, was correct in his claim that non-causal mathematical laws have replaced causal laws in theoretical physics. His mistake was to assume that the same applied to every advanced science. This is an instance of a saying of Wittgenstein’s (1953, § 593):

A main cause of philosophical disease – a one-sided diet: one nourishes one’s thinking with only one kind of example.

It also shows that one must study history and philosophy of science, and not philosophy of science without the history. Only the history of science can provide the variety of examples needed for philosophy of science.

To sum up then: Russell’s thesis appears to be true of some advanced sciences, e.g. theoretical physics, but false of others, e.g. medicine. This situation poses the following question: why is it that some advanced sciences can dispense with the use of causal laws, whereas such laws continue to play a central role in other advanced sciences? We will consider this question further later in the chapter, but now let us turn to a consideration of Collingwood’s views on causality.

1.2 Collingwood’s AIM theory of causality

In Collingwood’s 1938 paper on c...

Table of contents

• Cover
• Half-Title
• Title
• Copyright
• dedication
• dedication1
• Contents
• Acknowledgements
• Preface
• Introduction
• PART I Causality and action
• PART II Causality and mechanisms
• PART III Causality and probability
• Appendix 1: Example of a simple medical intervention which is not an intervention in Woodward’s sense
• Appendix 2: Mathematical terminology
• Appendix 3: Sudbury’s theorems
• Glossary of medical terms
• References
• Index