Which fallacy mistakenly assumes that because an event precedes another event it caused it?

John Oliver uses humor to show how the vaccine debate stems largely from a causal fallacy.

John Oliver’s Last Week Tonight discusses the sensitive topic of vaccine fears and the misconceptions around them. Opposition to vaccines is frequently based on the Post Hoc Ergo Propter Hoc fallacy as the symptoms of autism appear at the same age that vaccines are normally injected. This episode provides a great example of how confusing temporal order with causality can cause real world harms like undermining public health.

One possible segment to play in class is 14:13-19:13.

Distinguishing good reasoning from bad is a central learning objective in a critical thinking course. Logical fallacies are an essential element to this, but students run the risk of misunderstanding the significance of logical fallacies. They often think of them merely as cards to pull during an argument, like a referee in a soccer game. They do not think of them as persistent and common bad habits in our thinking. John Oliver frequently uses the platform of his show to reveal some of these dubious forms of reasoning found in everyday public discourse. I use his episode on vaccines to offer a concrete example of logical fallacies with tangible social harms to my students.

I understand critical thinking courses as addressing three important needs for students. First, cultivating the student as an individual thinker. Are they able to use reasoning effectively in their own lives or careers to make good choices? Second, preparing the student to better reason with others to advocate their perspectives and interests. Are they able to give good reasons for their positions, and use solid arguments to articulate their viewpoint and advocate for themselves or others? Thirdly, empowering the student to become a good citizen. Are students growing into individuals able to make good, free choices in a civil society without being misled? Do their actions as a citizen make others happier and healthier?

My use of comedy keeps these three goals in mind. First, the scenes I chose contribute to the student’s ability to think more clearly by offering a concrete example of fallacious reasoning in public discourse. Second, they also show examples of what not to do if one hopes to think critically. Third, and most importantly for me, these scenes clearly demonstrate the negative public risks of bad reasoning.

The season 4 episode 17 on fears over vaccines demonstrates important fallacies in causal reasoning. The social and public health harms of anti-vaccine views were plain well before the pandemic, but a large part of the population has nonetheless gravitated towards these views. Likewise, poor media reporting on scientific and medical studies can be hugely misleading for the public. As such, I hope that by exploring these ideas, I can help my students to be better citizens. I do not want to do this in a confrontational way, as attacking people for holding anti-vaccine views will further shut down people’s critical thinking abilities by making them defensive. Instead, I merely want to offer a comic take on the reasoning process and where it goes wrong.

The post hoc ergo propter hoc (after this, therefore because of this) fallacy describes a confusion between the temporal order of events, and their actual causal order.

In other words, because event A preceded event B, then event A must have caused event B. In a critical thinking class, it is easy to come up with obvious and absurd examples. For instance, Bill and Monica both turned 18 before graduating high school, therefore their 18th birthdays caused their high school graduation. The problem with these sorts of easy examples is that they are also obviously wrong. As such, students might be misled into thinking that the fallacy is always that easy to identify. They might also miss how their own psychology might motivate our vulnerability to such poor forms of reasoning.

Vaccine fears are often a form of post hoc ergo propter hoc fallacy. To put it simply, children get a battery of vaccines from their birth until at least 2. As vaccines are effectively neutered or “harmless” germs, they can cause mild immune responses (or in the case of a few unlucky children, more harmful complications). They generally do not cause severe harm in patients, however children who are on the autistic spectrum often start showing their symptoms at around the same age. This motivates people to see a causal link that is not there simply because of the temporal order. A Lancet study in the 90s by a Dr. Wakefield (who has had his medical license since revoked) gave a veneer of empirical credibility to this mistaken intuition. This fed into a longstanding fear of vaccines going back to their invention. It turned out people were quite reasonably uncomfortable being exposed to the pus from smallpox infections from cows and milkmaids.

In a way, the response of parents is somewhat rational (or at least, seems to be) even if it is ultimately fallacious. After all, their children seemed fine until they got the vaccine. The vaccine then caused some minor responses like fevers or just general illness. Finally, the child starts showing full-blown autism symptoms. From the parent’s point of view, the only obvious relevant and notable event that preceded the autism diagnosis was the vaccination. Hence, the parent asserts a causal link, which was only bolstered by the content of Wakefield’s study. These parents, all sharing the same mistaken causal conclusion, then grouped together in a community that validated their belief.

This is a sensitive and charged topic. Those concerned with public health often charge that anti-vaccine ideas endanger others, and as such people who do not vaccinate their children aren’t simply making a factual error but a moral miscalculation. On the other side, parents who object to vaccines feel attacked for simply caring about their children. As this is a clear case where bad reasoning has concrete harms on public health, it is important to teach this as a failure of critical thinking, but not in a way that alienates students who mistrust vaccines. Especially for those educating in a community college with older students, it is quite possible that your students will be parents. It is also possible that they will be wrestling with the decision of whether to vaccinate, and they may hold doubts about the safety. If they feel attacked as ignorant or immoral for their doubts, then we are not doing our job as educators. If they feel comfortable questioning their doubts and seeing how they are mistaken, then we are succeeding.

The advantage of the comedic medium is first in the self-deprecation of the comic. Oliver, like many of those who gained their professional status under Jon Stewart in the Daily Show, are ruthlessly self-critical. This demeaning of the self by the comic disarms the viewer such that the viewer is more comfortable recognizing their own errors. The comic’s own self-deprecation serves as a powerful reminder of our own limited horizons.

The Teaching and Learning Video Series is designed to share pedagogical approaches to using humorous video clips for teaching philosophy. Humor, when used appropriately, has empirically been shown to correlate with higher retention rates. If you are interested in contributing to this series, please email the Series Editor, William A. B. Parkhurst, at

Sam Badger

Sam Badger is currently working on his PhD in philosophy at the University of South Florida in Tampa. He was born in London, England, and moved to California before getting his BA at University of California Santa Cruz and his MA at San Francisco State University.

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