False Cause: Post Hoc Ergo Propter Hoc
Bertha Alvarez Manninen
Homer: Not a bear in sight. The Bear Patrol must be working like a charm. Lisa: That’s specious reasoning, Dad. By your logic, I could claim that
this rock keeps tigers away.
Homer: Oh, how does it work?
Lisa: It doesn’t work. It’s just a stupid rock. But I don’t see any tigers
around, do you?
Homer: Lisa, I want to buy your rock.
The Simpsons, “Much Apu About Nothing”
In general, the false cause fallacy occurs when the “link between premises and conclusion depends on some imagined causal connection that probably does not exist” (Hurley 2015, 149). This is certainly the case when it comes to Lisa’s rock - there was no evidence that the rock itself was keeping tigers away from Springfield. By the same logic, it could have been her beaded necklace or Bart’s skateboard that was keeping the tigers away.
There are three different ways an argument can commit the false cause fallacy: post hoc ergo propter hoc; cum hoc ergo propter hoc; and ignoring common cause. We’ll deal with post hoc ergo propter hoc here. Also see the chapters for cum hoc ergo propter hoc (Chapter 78); and ignoring common cause (Chapter 79).
Consider Sheldon’s words from an episode of The Big Bang Theory titled “The Electric Can Opener Fluctuation”: “No, Mother, I could not feel your
church group praying for my safety. The fact that I am home safe does not prove that it worked, that logic is post hoc ergo propter hoc.” This Latin phrase literally translates to “after this, therefore because of this.” It is committed when one argues that a causal relationship exists between A and B mainly because A happened before B. On The Big Bang Theory, Sheldon notes that his mother commits the post hoc ergo propter hoc fallacy when she attributes his safe return from an expedition to the prayers of her church group, for it is not the case that Sheldon’s returning from his expedition safely is sufficient evidence for establishing that the prayers worked.
Athletes also often commit the same fallacy when they attribute winning an event to an article of clothing that they wore during the event; the flaw in reasoning becomes obvious when one notes that that, by the same logic, the athlete could have attributed her win to the particular shampoo she used that morning while bathing. Or Sheldon’s mother could have attributed his arriving home safely to whatever breakfast food she had that morning. Though, of course, causes do precede their effects, this alone does not suffice to prove that there is a causal connection between two events. What is needed is actual evidence that two events have a causal connection.Some have argued that the use of marijuana serves as a precursor to the use of other, much stronger, drugs. Consider the words of Nick Kristof - quoted in Szalavitz (2010) - who is largely in favor of the legalization of marijuana: “I have no illusions about drugs. One of my childhood friends in Yamhill, Ore., pretty much squandered his life by dabbling with marijuana in ninth grade and then moving on to stronger stuff. And yes, there’s some risk that legalization would make such dabbling more common.” Yet many have argued that the notion of marijuana as a “gateway” drug is a result of the post hoc ergo propter hoc fallacy. While it may be true that people who are addicted to hardcore drugs at first started with drugs like marijuana, that alone does not suffice to show that the use of marijuana is what caused the use of the stronger drugs. Indeed, the Institute of Medicine of the National Academy of Sciences, while recognizing that marijuana use precedes the use of much stronger drugs, refutes any such causal connection.
In the sense that marijuana use typically precedes rather than follows initiation of other illicit drug use, it is indeed a “gateway” drug. But because underage smoking and alcohol use typically precede marijuana use, marijuana is not the most common, and is rarely the first, “gateway” to illicit drug use.
There is no conclusive evidence that the drug effects of marijuana are causally linked to the subsequent abuse of other illicit drugs. (Szalavitz 2010)The post hoc ergo propter hoc makes its appearance often in politics. In 2015, Senator Mitch McConnell attributed the improvement of the US economy to the fact that many Republicans had been voted into their positions during the midterm elections: “After so many years of sluggish growth, we’re finally starting to see some economic data that can provide a glimmer of hope; the uptick appears to coincide with the biggest political change of the Obama Administration’s long tenure in Washington, the expectation of a new Republican Congress” (Jacobson 2015). McConnell neglects to mention that the economy was already improving before the November elections and that it takes much more than two months after voting a party into office before any noticeable changes in the economy can be seen. In 2011, a Fox Nation headline read, “Stocks Tumble Worldwide after Obama Speech” (Wallace and Nazareth 2011), clearly implying that the president’s speech contributed to such a decline. Many individuals attribute the cost of gas prices to whichever president is in charge at the time, blaming his policies when gas prices skyrocket while giving him credit when gas prices are low. However, gas prices respond to a variety of worldwide economic conditions, not simply to the policies of one particular administration.
One example of the post hoc ergo propter hoc fallacy that has had a great impact on public health has been the recent fear of childhood vaccines, particularly the MMR (measles, mumps, and rubella) vaccine and the concern it can cause autism. The fear started in 1998 when Dr. Andrew Wakefield and 12 colleagues published an essay in The Lancet arguing that a correlation exists between the MMR vaccine and autism; the article was later retracted given that several elements in the study were either dubious or outright incorrect.
Yet the public had been scared. Celebrity Jenny McCarthy became a vocal opponent of the MMR vaccine, attributing her son’s autism to having received it: “If you ask a parent of an autistic child if they want the measles or autism, we will stand in line for the f***ing measles” (Klugar 2009). As a result of this public fear, there has been a substantial decline in the number of children being vaccinated against diseases like MMR and pertussis and an increase in such diseases within the general population. In 2014, the Center for Disease Control released a study that noted that measles in the United States have reached a 20-year high (Center for Disease Control). This is particularly dangerous not just for unvaccinated children but for individuals who cannot receive vaccinations due to autoimmune disorders and who therefore must rely on herd immunity to keep them healthy.Because children are often diagnosed with autism in early childhood, typically around the same time that the MMR vaccine is also administered, many people have attributed a child’s autism to the MMR vaccine. However, subsequent and repeated studies have shown that there is no causal connection between vaccinations and autism (see, for example, Myers and Pineda 2008). Therefore, this is an example of the post hoc ergo propter hoc fallacy because the mere fact that the vaccine is administered closely before autism is diagnosed is taken as evidence that the former caused the latter even though there is simply no actual evidence that this causal connection exists.
References
Center for Disease Control. 2014. “Measles Cases in the United States Reach 20-Year High.” http://www.cdc.gov/media/releases/2014/p0529-measles.html (accessed October 3, 2017).
Hurley, Patrick. 2015. A Concise Introduction to Logic. Stamford, CT: Cengage Learning.
Jacobson, Louis. 2015. “Mitch McConnell Says Economic Uptick Coincides with Expectation of GOP Senate Takeover.” Politifact, January 8. http://www.politifact.com/ truth-o-meter/statements/2015/jan/08/mitch-mcconnell/mitch-mcconnell-says- economic-uptick-coincides-exp/(accessed October 3, 2017).
Klugar, Jeffrey. 2009. “Jenny McCarthy on Autism and Vaccines.” Time, December 15. http://content.time.com/time/health/article/0,8599,1888718,00.html (accessed October 3, 2017).
Myers, Martin, and Diego Pineda. 2008. Do Vaccines Cause That?!: A Guide for Evaluating Vaccine Safety Concerns. Galveston, TX: Immunizations for Public Health.
Szalavitz, Maia. 2010. “Marijuana as a Gateway Drug: The Myth that Will Not Die.” http://healthland.time.com/2010/10/29/marijuna-as-a-gateway-drug-the-myth- that-will-not-die/(accessed October 3, 2017).
Wallace, Stuart, and Rita Nazareth. 2011. “Stocks Tumble Worldwide after Obama Speech.” Fox News, September 9. http://nation.foxnews.com/obama-jobs- plan/2011/09/09/stocks-tumble-worldwide-after-obama-speech (accessed October 3, 2017).