10 Common Logical Fallacies Everyone Should Know
Examples
Henry is talking to his group of friends about how not only are vaccines especially effective at preventing disease [1], but they are also immensely safe as well according to science. Following Henry's remarks, one of his friends comments:
P1: Henry got a C on his Chemistry test last week.
C: So, he clearly doesn't understand science well and is wrong here about the science.
Explanation: While it is important to question a source's credibility, a proper response from Henry's friend would have been to address the statement regarding vaccine safety and efficacy. In other words, the C that Henry received on his Chemistry exam is not an adequate reason to dismiss Henry's claims.
Person 1: Unequivocally, the Earth is round. Countless observations have been made along with countless measurements proving that the Earth is indeed round.
Person 2: You're not much of a free thinker are you? Your years of schooling, indoctrination as I like to call it, are clouding your judgment. Do you really believe NASA doesn't manipulate the images to suit their agenda? The Earth is definitely flat.
Explanation: Person 2 has distorted what Person 1 said to a degree that is almost laughable. Nowhere in Person 1's statement did he/she mention anything about NASA or the formal education system. The term “free thinking” is often used by individuals who embrace conspiratorial thinking in an attempt to rationalize holding a fringe view that is typically unsupported by any evidence. Person 2 has blatantly committed a straw man fallacy.
P1: Albert Einstein was an expert physicist.
P2: He came up with the theory of relativity.
C: Therefore, the theory of relativity is true.
Explanation: While Einstein was indeed an expert physicist, earning a Nobel for his work on the photoelectric effect, we shouldn’t believe something just because he said it is true. There are reasons to believe Einstein was correct: his theory explains the orbit of Mercury, GPS systems work, and gravitational waves have been observed [2,3,4]. All of these reasons validate support for relativity without reliance on the authority of Einstein.
P1: If I lend Jon money, then he will most certainly tell his friend Alex about it.
P2: Next, Alex will be asking me for money.
P3: Regardless if I give Alex money or not, he will then go on to tell his friends that I lent Jon money.
P4: Once Alex's friends know, they will go on to tell all of their friends and, eventually, the entire neighborhood will be asking me for money.
P5: The problem will get so bad that I will have to lock myself in my house as people will constantly be harassing me for money.
C: Ergo, I shouldn't lend Jon a single penny.
Explanation: This scenario is incredibly unlikely to unfold to this extreme if I were to lend Jon some money. Yes, a few more people may find out about it if the amount of money is large, but the probability of the chain of events going to the extreme of needing to board myself in my house is very small. That said, if I had just won the lottery, this argument would be stronger than if I were to lend someone $20.
Appeal to Popularity:
Have you seen the new challenge going around the Internet? It’s called the paperclip challenge.
You stick a paperclip into an outlet and try not to get shocked.
It’s going viral right now and everyone is uploading videos of themselves doing the challenge.
We should do it!
Explanation: It is evident that this argument is appealing to the popularity of something to justify participation in the behavior. Obviously, sticking metal objects into an outlet is a very bad idea regardless of whether or not it’s popular.
P1: Apples and Oranges are both fruit and they're both round.
C: Therefore, they must taste the same.
Explanation: The fact that Apples and Oranges are both fruit and that they're round (i.e., they are equivalent in these characteristics) doesn't necessarily mean that they are then going to taste the same. From everyday experience, we know that Apples and Oranges do not taste the same.
You will often find science deniers exploiting the concept of “proof” when it comes to the scientific method. The argument will go something like this:
P1: Only 97% of the world's scientists agree that humans are causing global warming, which means that there are still 3% who disagree.
P2: Because the agreement is not 100%, human-caused global warming remains unproven.
C: Therefore, we cannot say for sure whether or not humans are really causing global warming.
This script is used repeatedly by deniers to sow doubt in whatever area of science they please. A more generic script that could be applied to any area of science would look something like this:
P1: Only [insert percentage of world's scientists who agree here] agree that [insert scientific topic of interest here], which indicates that [insert percentage of dissenting scientists here] disagree.
P2: [insert scientific topic of interest here] remains unproven because all of the scientists clearly don't agree.
C: Therefore, we cannot say for sure whether [insert scientific topic of interest here] is true or not.
Explanation: Within science, the concept of “proof” does not exist in the same sense as it does in mathematics or logic. When you say that something is “proved” within math or logic, it can be taken as immutable, but in science, this isn't the case. Science can be viewed as a method that helps us to asymptotically approach objective truth (i.e., something that is absolute), but we can never claim to know anything with 100% certainty*. Hence the reason why “prove” is verboten within science and the phrase “scientific proof” or “science has proven x,y, or z” is not technically correct to use. All that said, science is the best instrument that we have for distilling truths about our world (i.e., it helps us to be less wrong about the world around us) and the best decisions can only be made when we acknowledge the best available evidence that is being provided to us by the scientific method.
*While it would be irresponsible to claim 100% certainty, we can, however, make claims vanishingly close to it. This is an example where a hypothesis becomes a scientific fact as it is firmly supported by volumes of evidence (e.g., anthropogenic global warming).
P1: Vaccines contain the preservative thimerosal, a mercury preservative, which can cause autism as demonstrated in [5].
C: Ergo, vaccines should be avoided as they can cause autism.
Explanation: Here, I am clearly cherry picking as I've only including one paper and when compared to the full body of evidence, thimerosal-containing vaccines don't cause autism [6]. Furthermore, this paper engages in a fair amount of speculation and isn't actually conducting an experiment, statistical analysis, etc. in order to better understand a possible mechanism between mercury exposure and autism. The entire paper is referencing other studies and frequently uses words such as “maybe, possibly, potentially, etc.” throughout. Overall, the paper doesn't say much other than “more studies are needed,” which the untrained eye would probably miss and mistake this paper as presenting conclusive evidence that mercury and/or thimerosal in vaccines are linked to autism.
Candidly, I would often use many different studies in my arguments surrounding vaccine safety. However, for didactic purposes, I thought it would be appropriate to demonstrate true cherry picking where I am only using one study to support my position. Reflecting on the studies that I used in the past, I can assure you that all of them have their flaws or weren't saying what I thought they were saying.
You often find superstitious types of behavior within sports. From lucky rabbits feet to choosing never to wash socks, sports of all types have individuals engaging in this type of behavior. For example, consider a young man by the name of Bill who is an avid Chicago Black Hawks fan. One day, he was watching a game with his family and was sitting at a particular spot at the dinner table during the game. The Black Hawks ended up losing that particular game that Bill wanted them badly to win and due to this loss, he decided to blame the position at the dinner table that he was sitting at. Since that particular loss, he refuses to sit at that particular position at the dinner table as he's convinced that it's “bad luck.” That is, his sitting at that particular seat at one point during the game is to blame for the loss. This narrative in argument form is:
P1: The Chicago Black Hawks lost the game.
P2: During the game I was sitting at position x at the dinner table.
C: Hence, position x is responsible for the Black Hawks loss and is “bad luck” in general.
Explanation: Bill is attributing the Blackhawk's loss to where he sat during the game. There are no credible scenarios that come to mind that would remotely support the hypothesis that where you sit in your home during a game would have any impact on a hockey team's performance. Clearly, Bill is falsely assigning blame to the seat for the loss.
Consider the following argument in regards to the COVID-19 vaccine:
P1: I didn't get the vaccine and have contracted COVID twice now.
P2: Both times it felt just like a cold and I recovered quickly.
C: Therefore, you really don't need the vaccine.
Explanation: While it's unfortunate contracting COVID twice, it's fortuitous that both cases were relatively mild given the vaccination status. However, just because the experience was mild without vaccination, doesn't mean that this will always translate to the experience of others. People have unique physiologies and there are multifarious aspects to human health. This is why scientific inquiry is so important as it will reveal, on average, how people respond to a particular disease as well as any medical interventions that are available to treat it. By harnessing the power of statistics, a better systemic view can be derived from which an optimal plan of action can be formulated.
References
[2] Sutter, Paul. Why Relativity's True: The Evidence for Einstein's Theory. Space.com (2018).
[6] Centers for Disease Control and Prevention. Frequently Asked Questions about Thimerosal.