How can we know if something causes something else? What is the difference between a sufficient cause, a necessary cause, and a risk factor? How can we avoid traps in understanding causes and non-causes?
By Mark D. Harris
An acquaintance, a devoted Catholic, shared with me a text conversation that he had with his son last weekend. It caught my attention, so we discussed it at the dinner table at our house Wednesday night.
Father: R U going to be home to go to 9:30 mass or 1115 or 5PM?
Teenage son: Will’s here, can I just not go this week?
Father: No, that is not an option. Will can come if he likes.
Son: The Catholic church has survived the ages by creating wars, having corrupt leaders, and blaming our problems on others. I think that supporting an establishment that has built itself on hypocrisy is something that you shouldn’t encourage me to do. God can be found in all things, right? Then why do we bow to marble tables while destroying the world he made with pollution?
Father: I would love to have a philosophical discussion with you on this topic, but texting is not my preferred medium. In the mean time you will come to mass, not because your presence is something that either God or the Church needs but because 1) it is best for you, and 2) because I am telling you to come.
Son: I’m about to go to a week in the woods! That’s the holiest thing I can do…Can you pick us up at 11?
This interaction is interesting on many levels. It demonstrates communication between a father and his son, and suggests real affection and a good relationship between the two. Not knowing the son, it is impossible to know whether he actually believed what he said about the Catholic Church or whether he was simply trying to spend more time with his friend and get out of going to Mass. Perhaps a little of both? For the sake of discussion, let us assume that the boy was at least partly serious about his allegations.
My family’s dinner discussion that night focused on the son’s initial response. I teach my children to logically evaluate all statements that claim to be fact, including those of this young man. For the purposes of our conversation we assumed that these statements about the Catholic Church implied causation. This means, for example, that the Catholic Church caused wars, caused corrupt leaders and blamed their problems on others purposefully to help them survive.
First, we wonder where this young man got these ideas about the Church. Most people who develop negative impressions about an institution they belong to do so on the personal level. A person might say “the church is unfriendly” or “the priest is boring” from their own experience, but most people do not have personal experience with their church “creating wars”. Therefore he must have gotten at least some of these ideas from someone else. The media and public schools have plenty of negative things to say about the church so it is easy to suspect that they are the source, but we cannot be sure.
Second, if these statements imply causation, then we must begin by saying a little about causation. Webster’s definition of “cause” is “something that brings about an effect or a result.” The world of public health provides a more comprehensive explanation. There are only three types of causation. The first is the necessary cause, which means a cause that must be present to bring about a certain result. Infection with mycobacterium tuberculosis (mTB), for example, is a necessary cause for the disease tuberculosis. That means that it is impossible to develop the clinical disease of tuberculosis without being infected with mTB.
The second type of causation is the sufficient cause, which means a cause that inevitably brings about a certain result. While mTB is necessary to cause clinical tuberculosis, it is not sufficient. Many people are infected with mTB without ever developing clinical disease. Sticking one’s unprotected finger into an open flame is sufficient to cause a finger burn; every time someone does it a burn will result. However, it is not a necessary cause; it is possible to burn one’s finger without sticking it into an open flame.
The third type of causation is the risk factor, which means that exposure to a certain cause is more likely to bring about a certain result. Smoking is not a necessary cause for lung cancer; non-smokers can develop it. Smoking is not a sufficient cause for lung cancer; some people smoke for decades and never get lung cancer. However, smoking increases the risk of lung cancer 10-fold, meaning that smokers develop lung cancer 10 times as often as non-smokers. Most things that people consider causes are actually risk factors that increase the chance of something happening. In an extreme example, getting shot in the head is neither necessary nor sufficient to cause death. Some people who are shot in the head survive and many people die without ever being shot in the head. However, it is a large risk factor for death; the chances of death after being shot in the head are much greater than the chances of death without being so injured. In a murder investigation, the homicide detective and the coroner will list “shot in the head” as the cause of death, not a risk factor.
Using risk factors to prove causation is much more difficult than evaluating necessary or sufficient causes. What degree of increased risk is necessary to call a risk factor a cause? If exposure X makes outcome Y 10 times more likely, as smoking does with cancer, we call it a cause. But what about if exposure X makes outcome Y only 10% more likely? Is X then a cause of Y? If not, where do we draw the line?
We must now apply these truths about causation to the young man’s suppositions noted above. He suggested that the Catholic Church caused wars. If the Church was a necessary cause we would expect every war in history to have been caused by the Catholic Church. Since war has predated the Catholic Church by millennia and since many wars have occurred in circumstances wholly unrelated to the Church, it is foolish to consider the Catholic Church as a necessary cause for war.
If the Catholic Church were a sufficient cause for war, we should expect there to be war everywhere we encounter the Church. Judging by the historical record and our current experience we conclude that this also is untrue. There have been many circumstances in which the Catholic Church has existed without war at all.
Is the Catholic Church, or any church for that matter, a risk factor for war? In order to prove that, we would need to perform a study, just like when evaluating any other risk factor. The study question would be something like “Are areas in which the Catholic Church is present more likely to experience wars than areas in which the Church is absent?” The null hypothesis would be “There is no difference in the likelihood of war in areas exposed to Catholicism than in areas not so exposed.” The alternative hypothesis would be that a difference does exist. The exposure of interest would be “exposure to the Church”, the outcome of interest would be “wars”, and the study population would need to be similar in every (or at least most) other respects.
The first and second conditions are hard to meet because it is difficult to define “exposure to the church” and “war”. Does “exposure” mean that one has read the Bible, that a certain percentage of people in an area are Catholic, or something else? Does “war” mean Clausewitzian total war, pitting entire peoples against each other in a conflict to the death, a primitive ceremonial war, or something in between? The final condition is hard to meet, because finding two sizeable populations of similar age, sex, ethnicity, wealth, education, and other characteristics, one of whom was exposed to the Catholic Church and one of whom was not, is difficult. Nonetheless, insofar as it can actually be accomplished, given the reporting bias of history and other limitations, there is no convincing evidence that Christianity of any stripe is a risk factor for wars.
Therefore the statement “creating wars” has no objective basis in fact; it is merely opinion. One could and should perform the same analysis for the statements “having corrupt leaders”, “blaming our problems on others”, “building itself on hypocrisy”, and “destroying the world with pollution”. Doing so leads to the same results. These statements are matters of opinion; not of fact. Our teenage friend is certainly entitled to his opinion, as we all are, but his statements carry no authority of truth.
Hopefully the sources of this information, whether the media, the schools, or somewhere else, understood this when they presented this information to him, and presented it as such. Authority figures such as teachers are especially likely to have their statements taken as truth without the appropriate evaluation, so they must be careful to explain their statements and the reasons behind them.
The father undoubtedly hopes that his son was merely making excuses to spend more time with his friend, and so do we. Nonetheless, their interaction provided a valuable opportunity for my family to learn about how to analyze supposed statements of fact. We are grateful for the chance. We also hope that he advances in holiness, and in fun, while in the woods.