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Reality

Coronavirus, Correlation & Causation

Martin Jenkins uses the virus to test our knowledge of causation.

Because of the coronavirus, the skies are bluer, and my vision has improved.

Do those assertions sound crazy? Well, they probably do; but I can demonstrate that they are, if not literally true, logically justifiable. It is an undoubted scientific fact that one result of the lockdown was a severe reduction in travel – both flights and on the ground. As a result, pollution levels have dropped significantly, and so the sky is bluer than usual for want of haze. Also, that lack of haze means that I can look out of my bedroom window, and, for the first time in thirty-four years, see clearly to the horizon – in my case, several miles away in north London. So my vision has improved, in the sense that I can see further than I used to.

Now if we choose to be pedantic, it could be said that these effects are not caused by Covid-19 but by our response to it. But on the other hand, if Covid-19 hadn’t happened, our response of less traffic would not have happened, and so the effects would not have happened; so the effects lie at the end of a chain of causation which begins with Covid-19. In other words, without Covid-19, these things would not have happened, so it is legitimate to describe Covid-19 as (in some sense) the cause of these effects.

Human beings are not particularly well equipped to understand causation. We tend to think in post hoc, ergo propter hoc (‘after that, therefore because of that’) terms. C.S. Lewis came up with a brilliant counter-example. A signal sounds in a quarry to announce an explosion. Does the signal cause the explosion? Of course not. But, does the explosion cause the signal? Well, yes, in a sense… But how can something that happens after an event cause that event? The answer is, of course, that the human intention of the explosion causes the signal; and it is in this sense that the explosion causes the signal which precedes it.

Our understanding of causation also tends to be linear and singular. To take the latter first: we are inclined to think that a single cause x causes single effect y. But as we have seen in the case of Covid-19, cause x has produced multiple effects, many of which were not foreseen or intended. As for linear effects, the quarry example demonstrates that these do not necessarily work. That example shows that our usual assumption – that causation cannot work backward in time – fails in the face of human intention. In other words, once we decide to take action, then in respect of our behaviour we create the possibility of a non-linear understanding of causation. So, we can draw a line from coronavirus to blue skies – but it will not be a straight line, and will have to take in some other things on the way.

This will possibly be reminiscent of Aristotle’s theory of causation. Aristotle, it may be remembered, argued that there were four ‘causes’ involved in any event, that is, in the creation or altering of any object:

• The ‘material cause’ – the physical composition of something

• The ‘formal cause’ – the design into which the material is shaped

• The ‘efficient cause’ – the action which shapes the thing

• The ‘final cause’ – the purpose behind the thing or event

I’ve put ‘cause’ in inverted commas here because it is a mistranslation of what Aristotle said. In the Middle Ages the Greek word aition was rendered by the Latin word causa, and this gives us the English ‘cause’. However, a better translation of aition might be ‘factor’. Aristotle was identifying the factors involved in producing any result.

In Time We Trust by Friedrich Farshaad Razmjouie, 2021

It should be said that Aristotle’s system works best for deliberately created artefacts (physical or otherwise). Take, for example, a chair. The ‘material cause’, the wood, is the starting point. The ‘formal cause’ is the idea of making a certain chair out of it with the design of that chair; and doing the actual carpentry is the ‘efficient cause’. Finally, the chair is made for the purpose of being sat on, its ‘final cause’. Unfortunately, this system breaks down severely when applied to natural phenomena. Organisms do have ‘final causes’ – to survive and reproduce – but the theory of natural selection denies any ‘formal cause’. Adaptation by natural selection through random mutation is not any sort of design. Equally, an earthquake or a thunderstorm does not have a ‘final cause’ or purpose. They just happen, as a result of a concatenation of things and circumstances.

A mantra of statisticians is that ‘correlation is not causation’. Just because events and phenomena march together does not mean that one causes the other (even though our linear thinking would like such an explanation). However, high degrees of correlation should make us look for chains of causation which explain the correlation. When I was doing social work in rural Shropshire, I was surprised by the fact that the professions with the highest suicide rates were doctors and farmers. What is it in the psychology of these professions that makes them prone to kill themselves? Actually, nothing. But doctors have access to drugs, and farmers to shotguns, and in both cases know how to use them, so they are more likely to succeed in killing themselves. Other professions may well have higher rates of attempted suicide, but our statistics are based on the records we keep, and those only record the deaths and the reasons for them. However, this does illustrate that correlation is not causation.

The bluer skies during lockdown might have been interpreted as a mere correlation, or even a coincidence. How could a virus affect air quality? Well, a chain of causation has already been demonstrated; but perhaps it can best be expressed negatively. If Covid-19 hadn’t happened, there would have been no lockdowns; pollution levels would not have fallen; and we would still be staring through hazy skies at rather grey distances. Correlation is not causation; but the fact that two or more things are statistically correlated should make us ask the question: Is there a chain of causation which accounts for the correlation?

The biggest problem with Aristotle’s four ‘causes’ is that the theory makes no allowance for the most basic principle in causation: the Law of Unintended Consequences (sometimes expressed as ‘You can never do only one thing’). His ‘final cause’ implies that there is a single end or result to which any causation is leading. This does not address the reality that there other results implicit to the process. These results are not intended, but they happen anyway. If a thunderstorm had a purpose, it would probably not include starting a forest fire; but it happens anyway. Human action is possibly the biggest, certainly the most consistent, source of unintended consequences. The government only set out to contain Covid-19; it accidentally improved air quality in doing so.

Medical research routinely tests for side-effects. This is perhaps exceptional among human endeavour. Usually we blunder ahead with a clear goal in sight, and never pause to ask ‘What are the other consequences going to be?’ This is a consequence of our tendency to think about causation in linear and singular terms. We can only see the desired result and the straight line leading to it. But that straight line is a trunk, and we ought to try to see the branches as well.

Emergency legislation is usually the product of linear thinking. Recent emergency legislation produced the unintended consequence of the improvement of air quality. Usually, the unintended consequences are negative. As an example, I cite the UK’s 1939 ‘Defence of the Realm Act’, which allowed the detention of German citizens living in Britain. As a result, numbers of German Jews who had fled Nazi persecution were detained, presumably because the authorities saw them as a potential nucleus of a Nazi conspiracy, rather than as people who could help in the fight against Nazism. As Schiller wrote, “Against stupidity the gods themselves contend in vain.”

The late Martin Jenkins was a Quaker, a retired community worker, and a frequent contributor to Philosophy Now. We publish this article in tribute to him.