Appellate Advocacy Blog

Editor: Tessa L. Dysart
The University of Arizona
James E. Rogers College of Law

Thursday, March 15, 2018

Thinking Thursdays: Know your logical fallacies (Part 1)

Ruth Anne Robbins, Distinguished Clinical Professor of Law, Rutgers Law School

Faulty reasoning undermines the substances of a legal argument as well as the credibility of the advocate. After a quick search of the online briefs available on Westlaw and Lexis, I can safely tell you that several thousand appellate briefs reference logical fallacies—typically as a precursor to a direct refutation of an opposing party’s argument. How many of us these days know our logical fallacies as well as we should?

Beyond calling out opposing counsel for these errors, the wise attorney also tests their own writing to see if they have relied on fallacious thinking. In most logical fallacies, something has gone wrong with the legal syllogism. In a sense, the major premise of a syllogism is a rule, while the minor premise is a fact. The conclusion flows from the application of the rule to the fact. Here is a simple example.[1]

            Major premise:          The speed limit where defendant was arrested is 45 MPH.

            Minor Premise:          The working-perfectly radar gun clocked defendant at 63 MPH.

            Conclusion:                Defendant was speeding

In most logical fallacies, some part of the syllogism fails. There are four major categories of logical fallacies in law. Today’s blog entry goes through the first two groups of common fallacies: the non-sequitur fallacies and the insufficient evidence fallacies. The next Thinking Thursday blog entry will discuss two other categories: shallow thinking and avoidance fallacies.  

Logic 21. Non-sequitur fallacies. In a non-sequitur, the major premise is applied incorrectly to the minor premise. You can recognize these when the conclusion does not logically flow from the premise

1.1  The correlation equals causation fallacy commonly appears with statistical analyses. The arguer claims that because A and B appear together A must have caused B. The argument that the MMR vaccine causes babies to develop autism is a classic example of this type of fallacy. This amusing site shows these fallacies taken to the extreme.

1.2  The post hoc fallacy is closely related to the correlation/causation fallacy. The arguer claims that because A occurrence is followed by B occurrence, A’s occurrence must have caused B to occur. For example, after I ate an apple, I won an award—ergo, eating the apple caused me to win the award. In law, this sometimes shows up this way: When Pat drinks, Pat becomes violent. Therefore, Pat’s violence is caused by alcohol. That is a logical fallacy. Alcohol may lower inhibitions but does not cause violence by itself. 

2. Insufficient evidence fallacies contain faulty minor premises—faulty because they are false or based in inadequate material. There are three major types of these.

2.1  The hasty generalization fallacy happens when lawyers draw big and general conclusions from too small a sample size or from unrelated evidence. “Climate change has been solved because this winter New Jersey saw frigid temperatures in late December and early January, and because it saw two nor’easter storms in March.” In that example, the weather from one three-month period is being used to argue that a decades-old phenomenon is over or never existed. To show this syllogistically:   

Major premise: Climate change is making things warmer

Minor premise (flawed): weather over a three-month period matters to climate change

Conclusion (faulty): Climate change is over or solved.

2.2  The anecdotal evidence fallacy is related to the hasty generalization fallacy. The anecdotal evidence fallacy occurs when there is simply inadequate evidence to support the minor premise.

Major premise:  Some cities offer Segway tours of tourist areas.

Minor premise (flawed): I have never seen people on a Segway tour of Philadelphia.

Conclusion (faulty): Philadelphia does not have Segway tours.

2.3  Finally, shallow legal research can lead to the Texas sharpshooter fallacy. As a classic example, a person shoots an arrow at a barn wall, and then draws a bullseye around the arrow in the wall. That’s a logical fallacy and happens in the minor premise—i.e. “this is a target with a bullseye.” A Texas sharpshooter fallacy happens when someone builds legal analysis and argumentation around incomplete legal research. Think of this fallacy as related to a confirmation bias—when the legal researcher stops researching when they find a result that demonstrates the governing rule that they want for their client, versus what the rule might actually be.


It is easy enough these days to practice spotting logical fallacies simply by watching television. Many advertisements use fallacious reasoning in the marketing. Politicians will sometimes fall into the logical fallacy trap as well—watching the news for a week or two should net you a few examples. But, most importantly, review your own advocacy for these common errors.

] Thank you to Professor Ken Chestek (Wyoming) and Professor Steve Johansen (Lewis & Clark) for these examples. They come from the upcoming second edition of our co-authored textbook, Your Client’s Story: Persuasive Legal Writing (2d ed. Wolters Kluwer, expected publication date of later this year).

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This is somewhat useful, but more application of the fallacies to legal concepts would be much better. Also maybe focus a bit more on actual syllogistic fallacies (modus ponens, etc.) since you use syllogism in your examples?

Posted by: Kelsey Bernstein | Apr 19, 2018 2:28:20 PM

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