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5 Common Logical Fallacies and Why You Need to be Aware of Them

Originally posted on on January 15th, 2018

Photo by Kristina Flour on Unsplash

If we are to engage in the science of behavior analysis, we are bound to use the scientific method. Yet as human beings, we often fall into the use of logical fallacies.

What are logical fallacies and why should we care?

A logical fallacy is a flawed argument or error in reasoning that renders the argument invalid (Purdue, 2013). While evaluating information, it is important to be skillful in identifying these errors in critical thinking. As we guide parents through the maze of autism, fight insurance companies for coverage, or discuss different treatment methods with colleagues, having some knowledge in this area of philosophy will help us stick to our ethical code and maintain high levels of professionalism.

There are over 100 types of logical fallacies (Williamson, O., 2017), but below are 5 of the most common and how we may contact them in our field.

Ad Populum

People using this fallacy attempt to prove their stance is correct because everyone else does. It is an emotional appeal rather than a statement based on facts. If you’re driving with the traffic and everyone is going 20 mph over the speed limit, you might think “I can’t get pulled over, everyone is going over the speed limit”. This would be an ad populum fallacy, just because everyone is doing the same thing, it does not make your conclusion (that you won’t get a ticket) correct.

Advertisements use this all the time. When a company claims their brand of cereal is America’s favorite or that 9 out of 10 people use their product, they are attempting to prove how great their product is by saying everyone else thinks it’s great too. In Applied Behavior Analysis (ABA), we could find this being used in a variety of situations. Parents might want to try a new alternative treatment for Autism because everyone else is doing it, according to an article or news story. We may even use it when determining the best goals to write or assessments to use, like using the VB MAPP instead of the ABLLS because everyone at your clinic only uses the VB MAPP. It doesn’t automatically mean your wrong, it only means that your conclusion is incorrect based on your reasoning.

Appeal to Authority

Appeal to authority makes the claim that an argument is correct because a famous or powerful person believes its true. The assertions put forth by someone that is famous or powerful may be true, but we shouldn’t believe it solely based on their position. Dr. Mehmet Oz is a large proponent of alternative medicine, often claiming various products will make you lose weight, reduce stress, or even survive risky surgery (Business Insider, 2015). He has a huge following of people that believe the misinformation he’s spreading because he’s a doctor and heart surgeon. Despite his education and status as a doctor, most of those claims have little to no scientific evidence.

In the world of Autism, Jenny McCarthy stands out. If she was not a well-known celebrity, her claims that vaccines caused her son’s autism and it was cured with a gluten-free diet would be less effective without proof. We need to be aware of this logical error for ourselves as well. If a well known and respected Board Certified Behavior Analyst (BCBA) presents a new concept or therapy method, we need to make sure we evaluate it objectively, without having our feelings about the author affect our judgement.

Hasty Generalization

This fallacy occurs when an individual makes a sweeping generalization based on a very small sample.  We should all be aware of this fallacy when reading single-subject studies, but hasty generalization applies to our daily life as well. I didn’t like the lunch I had at Chilis so all food at Chilis is bad. The last ABA therapist only did Discrete Trial Training (DTT) and used a robotic voice, so all ABA therapists will do that. I read a study that showed 3 children with autism showed decreases in their maladaptive behavior after a Functional Communication Training with M&Ms as reinforcers.  Therefore rewards of M&M’s will work for all children with autism.

Parents, therapists, and even our clients are susceptible to such a misjudgment. Educational settings, flashcards, and even adults that look like teachers can evoke avoidance and escape behaviors through a CMO-R (conditioned motivating operation- reflexive) (Carbone, et. al., 2010). A child’s last teacher might have given her lots of difficult work with little to no reinforcement, therefore all teachers could signal a worsening of conditions.

Post Hoc, Ergo Propter Hoc

This long-named fallacy assumes that if ‘A’ occurred after ‘B’ then ‘B’ caused ‘A’. In other words, correlation equals causation. This is only looking at 2 terms of our 3-term contingency without taking into account other participating factors. This fallacy is used intentionally by many people trying to sway others with manipulated information or graphs, but can also be used due to lack of additional information. If I eat a chicken sandwich and get sick several hours later, I will likely assume I’ve gotten food poisoning from the sandwich, but it could also be a stomach flu.

This fallacy is a favorite of anti-vaxxers. Their child got vaccines and shortly after displayed signs of autism. However, we also need to make sure we consider this fallacy when we make decisions. When looking at a graph of behavior data and see a dramatic change in behavior one month, we need to include phase change or event lines to show if there were medication changes, family changes, or if the change was due to our intervention.

Slippery Slope

This argument avoids the real issue by pushing the opponent’s argument to extreme hypotheticals. This fallacy is a form of emotional fallacy through the use of fear. Politicians and extremists are known for using this tactic. “Candidate X wants to impose stricter laws for purchasing a gun. If he wins the election hardly anyone will be able to purchase firearms and they will start being confiscated. Then what’s next? Taking away your constitutional right to free speech?” We see arguments like these for any hot button topic, but any of us can fall into this way of thinking.

Well-meaning parents may use it out of concern for the future of their child. “Why does my 3-year-old need to learn to follow instruction? If I make them follow every instruction now, they’re just going to become compliant robots and anyone could take advantage of them.” With this logic, whether intentional or not, you can refute almost any claim. “You give your children ice cream?! Ice cream is full of sugar and fat which will increase their weight. Obesity-related conditions are the leading cause of preventable death in the US. Are you trying to destroy your kids future?” It sounds ridiculous when stated that way, but if this fallacy can make ice cream sound scary, imagine what it can do to more serious subjects.

We have an ethical responsibility to avoid logical fallacies that most people accept and overlook every day. Being aware of the various manipulations that are used can help you identify them in your personal and professional life. 


Brodwin, Erin. (April 20, 2015). 5 ‘quack treatments’ Dr. Oz has recommended that are totally bogus. Business Insider. Retrieved December 25, 2017 from

Carbone, V. J., Morgenstern, B., Zecchin-Tirri, G., & Kolberg, L. (2010). The Role of the Reflexive-Conditioned Motivating Operation (CMO-R) During Discrete Trial Instruction of Children with Autism. Focus on Autism and Other Developmental Disabilities, 25(2) 110-124.

Logical Fallacies. The Skeptic’s Guide to the Universe. Retrieved December 25, 2017 from

Nordquist, Richard (August 14, 2017). Common Logical Fallacies. Thought Co. Retrieved December 15, 2017 from

Skoskiewicz, Mark (May 22, 2011). 10 Common Logical Fallacies. MyGuru. Retrieved December 20, 2017 from

Weber, R., Brizee, A. (November 3, 2013). Logical Fallacies. Purdue Online Writing Lab. Retrieved December 20, 2017 from

Williamson, Owen. (2017). UNIV 1301 University Seminar: A Short Course in Intellectual Self-Defense. University of Texas at El Paso. Retrieved December 25, 2017 from


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