Where do superstitions come from? Will breaking a mirror, spotting a black cat, or walking under a ladder cause something bad to happen? Will knocking on wood, throwing salt over the shoulder, or hanging a horseshoe over a door bring good fortune? Each of these superstitions is a cultural idea about causation. A pessimist might say superstitions reveal the limitations of human intelligence. It is possible, however, that the tools of reason produce both good and bad results. Post-hoc arguments are prime examples of how humans wrongly attribute causes to events.
Definition of a Post-Hoc Argument
Imagine you’re lying in bed with a broken leg. A visiting friend asks how it happened. You tell this friend that you were walking on the sidewalk by a building under renovation. You remember seeing a shadowy figure moving around on the roof, but the figure slipped away as soon as you looked. You then heard a frightened shout, and a ladder fell from somewhere above, which knocked you down and broke your leg. Your friend then suggests that the shadowy figure may have made the ladder fall — either throwing it down or knocking it over and quickly running away.
Fig 1. - Who caused what?
You might want to believe this argument. You’re feeling angry about your unfortunate accident, and it's nice to put the face of a villain onto the pain that you're experiencing. You do, however, wonder if that explanation is too simple — conveniently filling the gaps in your knowledge of the events. Important details are unknown. Trying to be rational, you note that the shadowy figure may have been a misperception — you saw it only briefly. Giving your perceptions the benefit of the doubt, you note that you did not see the shadowy figure and the ladder together, and you admit that the two things could have been unrelated.
Without more information, any explanation of the cause of the falling ladder will be a post-hoc argument.
Post-hoc is the Latin term for “after this.” A better English revision might be “after-the-fact.” "Post-hoc" describes a way of explaining events in retrospect. Post-hoc reasoning pays attention to the order and/or simultaneity of events, attempting to explain how one or more of them was caused.
Post-Hoc Fallacy Argument
Post-hoc arguments often wrongly identify the cause of something when there is not enough information to properly understand what happened. Multiple events can happen closely together and appear like one caused the other. This faulty attribution of cause is called the post hoc ergo propter hoc fallacy.
Post hoc ergo propter hoc translates into English as “after this therefore because of this.” It describes the tendency to misperceive one thing as the cause of another when the two things simply happened close together.
Fallacy: a failure in reasoning due to faulty logic.
Fallacies of causation come from misinterpreting the ways in which causes and effects are related.
Common Problems in Causal Reasoning
Faulty post-hoc arguments are often the result of related problems in causal reasoning. In other words, errors occur when causal relationships are not understood.
Correlation is not causation
Since the causal chain is the most common type of causal reasoning, people often mistake common-cause, common-effect, and systemic relationships as causal chains. But factors can work together to produce a shared effect, as in the relationship between poverty and crime. This process is called correlation.
Violent video games cause violent behavior.
Fig. 2 - A virtual reality gamer. The relationship between aggressive behaviors and playing violent video games continues to generate controversy.
The popularity of violent video games has sown much concern among parents and teachers who debate whether children's exposure to violent media explains the origin of aggressive behaviors. Following much exhaustive research since the 1990s, the American Psychological Association has repeatedly confirmed that no sufficient link has been established between exposure to violent video games and the onset of aggressive behaviors.1
The line of reasoning connecting the two often neglects the ways in which playing video games and aggressive behaviors are correlated, meaning how they appear together in a larger web of factors. Violent thoughts and feelings often appear in people who lack stable and caring social networks, and the lack of healthy social relations is often associated with increased solitary activities, including media consumption. Therefore, aggressive behaviors and unhealthy media consumption are correlated in a larger social context. To claim that one causes the other is to commit a fallacy of causal reasoning.
An interesting example of correlation not being the same as causation is the relationship between ice cream sales and murder rates. Statistically, as ice cream sales rise, so do the number of murders in the area. But does one cause the other? In fact, both share the common cause of rising temperatures. As the weather gets hotter, more murders happen and more ice cream is sold.2
Non Causa Pro Causa
Non causa pro causa (often shortened to simply non causa) is often called in English questionable cause.
In English non causa pro causa translates as "not the cause for the cause," and it describes a general misinterpretation of a chain of events. A non causa fallacy mistakes the effect for a cause.
People with health insurance are more likely to visit the hospital and the doctor, where they then find out they have an illness. Therefore, health insurance causes people to have illnesses.
There is much overlap between the post hoc fallacy, the confusion of correlation and causation, and the non causa fallacy. The non causa fallacy, however, generally mistakes the direction in which the cause and effect are related. In the previous example, claiming that health insurance causes people to visit the hospital is a non causa fallacy because it mistakes the direction of the cause/effect relationship. Instead of causing people to be sick, health insurance allows people to seek medical care when they need it. People with health insurance can go to the hospital when they are sick, while people without health insurance will avoid hospital bills even when they need hospitalization.
Fig. 3 - A cause may be misunderstood.
Post-Hoc Argument Examples
Here's an example of a post-hoc argument.
A man has has a mysterious cough for months. His doctors have performed extensive examinations on him, but none can identify a medical or health problem, so they cannot treat it. One day, the man sleeps on the opposite side of his bed, and the next morning his cough suddenly disappears. He then argues: "Changing the side of the bed that I sleep on cured my cough."
It's important to be able to analyze such an argument.
Analysis
To properly analyze the man's claim, one must consider what is known.
- It is known that the man had a cough.
- It is known that the reasons for the cough were not the man's health.
- It is known that his cough suddenly stopped, and it stopped after he changed the side of the bed he slept on.
Next, one must identify what is unknown.
- The man's family medical history is unknown.
- The air quality of the man's bedroom is unknown.
- The original cause of the man's cough remains unknown.
- How changing the side of the bed would stop a cough remains unknown.
Then, one must identify what is possible.
- It is possible that changing the side of the bed cured his cough.
- It is possible that another factor, like the air quality of his room, may have affected his cough.
Finally, one must identify whether any of the possibilities can be supported by evidence.
- The man could then sleep on the original side of the bed and see if his cough returns.
- The man could also have the building materials of his house and the air quality of his bedroom tested.
To properly analyze the situation, one must take into account the situation's knowns, unknowns, possibilities, and evidence. To claim that changing the side of the bed cured the man's cough is a post hoc ergo propter hoc fallacy because there is no evidence to support it as the cause of the cough's disappearance.
The placebo effect is an interesting phenomenon related to causality.
A placebo is a substance with no actual active ingredient, or it is a treatment with no actual therapeutic intervention.
To test the effectiveness of new medicines and medical procedures, clinical trials often divide groups of patients into a control group (which is given a placebo) and a treatment group (which is given the medicine being tested). The researchers then compare the number of patients in each group whose symptoms were helped. There are always a number of people in the placebo group whose symptoms were helped by the treatment, even though there was no active ingredient in their treatment. This is called the placebo effect.
Why the placebo effect occurs is not very well-understood. In some cases, the fact that the patient is receiving any treatment at all allows the patient to feel cared for, and the change in their psychological well-being can have a healing effect.
Identifying and Avoiding a Post-Hoc Fallacy
English language courses and tests require students to read and evaluate texts, many of which are argumentative and may contain faulty reasoning. If you come across an argument that focuses on causal relationships, ask yourself what types of causal relationships could exist between each of the factors.
When writing your own essays and arguments, it is important to avoid committing these same fallacies. Pay close attention to the words you use to describe the relationships between things.
A short list of words and phrases which indicate cause/effect relationships:
- because
- consequently
- due to
- so that
- if…then
- consequently
- thus
- since
- for
- therefore
- as a result
If you cannot identify a cause that is supported by evidence at hand, then use hedging terms that suggest some doubt: "potential," "possible," or "likely." Support your claims with evidence and consider the possible disagreements your reader might have with your ideas. Being able to think one step ahead of your reader is the key to successful argumentation.
Post-Hoc Argument - Key Takeaways
- The term post-hoc means "after-this" and refers to claims made about events in the past.
- Post hoc ergo propter hoc is a logical fallacy that attributes a cause and effect relationship to things that may have simply happened close together.
- The causal chain is the most intuitive kind of causal relationship: one thing causes another which causes another.
- "Correlation is not causation" is a simple way of saying that just because two things are somehow related, it does not mean that one caused the other.
- In the non causa fallacy, the direction of the causal relationship is confused.
1 "APA Reaffirms Position on Violent Video Games and Violent Behavior." American Psychological Association. 2020.
2 Justin Peters. “When Ice Cream Sales Rise, So Do Homicides. Coincidence, or Will Your Next Cone Murder You?” Slate. 2013.
3 Henry K. Beecher. "The Powerful Placebo." Journal of the American Medical Association, vol. 159, no. 17, pp. 1602-1606. 1955.
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