Common Logical Fallacies and Cognitive Biases in Argumentation

Bandwagon/argumentum ad populum

An argument built around the belief that something is true (or false) because a lot of people believe it to be so OR an argument that suggests the idea that, because many people are making a certain choice, we should, too.

Appeal to Tradition/argumentum ad antiquitatem

Assuming that old and established practices or beliefs are best simply because they are established.

Post Hoc, Ergo Propter Hoc

A occurred. Then B occurred. Therefore, A must have caused B.

Slippery Slope/Camel's Nose

An argument that proposes that one first step, change, decision, etc., will lead to future extreme and/or horrible consequences—even though there is no credible evidence to support this conclusion.

Ad Hominem

Attacking the person (typically exploiting irrelevant personal flaws) who is advancing an argument rather than the argument the person makes.

Camel's Nose Fallacy

Once you let the camel peek his/her nose into the tent, soon the whole camel will be in the tent.

Hasty Generalization

Making an assumption about a group of people or drawing a conclusion based on information about or experiences with only a limited, inadequate sample.

False Dichotomy

The artificial reduction of all the choices available to only two, ignoring the nuances rather than acknowledging the range of possible positions.

Fallacy of Omniscience

Making an argument that would only be possible with the power of omniscience (knowing all).

Fallacies of False Equivalence

Comparing two things that are totally different and suggesting it's not fair to compare them.

Both-sides-ism

Someone simultaneously condemns and excuses both sides in a dispute by claiming that both sides are equally guilty of inappropriate behavior or bad reasoning.

Cognitive Bias

A systematic error in thinking that occurs when we are processing and interpreting information in the world around us in a way that affects the decisions and judgments that we make.

Fallacy of Moral Equivalence

Arguing that a problem, decision, misdeed, etc. is similar to another problem, decision, misdeed, etc. that is far worse or extreme, drawing a comparison that is inaccurate and unfair.

Example of Fallacy of Moral Equivalence

Comparing a current policy or event to the actions of Hitler or the Nazi party, which is often unfair and offensive because few actions match the scale and horror of that event.

Weak/False Analogy

An analogy that is a stretch and/or the similar characteristics of the two different things are not relevant to the argument being advanced.

Example of Weak/False Analogy

Arguing against a law restricting guns by comparing guns and hammers as both being tools made of metal parts, which is weak because 'metal parts' is not relevant to the argument.

Straw Man Fallacy

Ignoring a person's actual argument and substituting a distorted, exaggerated, or misrepresented version of the person's position.

Example of Straw Man Fallacy

Misrepresenting Senator Jones's argument against funding a wildlife center by claiming he wants to eliminate a vital species.

Sunk Cost Fallacy

Making the argument that we should follow through on an endeavor because we have already invested time, effort, or money into it, ignoring whether the current costs outweigh the benefits.

Example of Sunk Cost Fallacy

Continuing to eat ice cream because most of it has already been consumed, despite knowing it may not be good for you.

Appeal to False/Weak Authority

Using an alleged authority as evidence to advance an argument when the person or source is not really a credible authority on the facts relevant to the argument.

Cognitive Bias vs. Logical Fallacy

A logical fallacy stems from an error in a logical argument, while a cognitive bias is rooted in thought processing errors often arising from problems with memory, attention, attribution, and other mental mistakes we make as our brains attempt to encounter and simplify the information we're taking in.

Confirmation Bias

Lending extra weight to favor information that confirms our own beliefs and preconceptions, regardless of whether the information is true or credible.

Example of Confirmation Bias

Someone only reads or watches news from sources or channels that agree with his or her political leanings OR, when reading a nuanced argument about a subject, only using or pulling quotes (perhaps, even out of context), that support our position on the topic.

The Dunning-Kruger Effect

Named after research by Cornell University psychologists David Dunning and Justin Kruger, whose studies found that we often wrongly overestimate our knowledge or ability in a specific area for which we are unskilled or lack experience.

Illusory Truth Effect

Describes how when we hear the same false information repeated again and again, we often come to believe it is true.

Groupthink

A psychological phenomenon that occurs within a group of people in which the desire for harmony or conformity results in an irrational or dysfunctional decision-making outcome.

Cognitive Dissonance

When we avoid facts and information because they conflict with our beliefs and make us feel uncomfortable.

Example of Cognitive Dissonance

I love Nutella—the delicious hazelnut cocoa spread. But then a friend confronted me with information about how the company that makes the product relies on palm oil, which is extracted by cutting down trees from palm tree plantations in Borneo and Sumatra, the only two places where Orangutans live.

Proportionality Bias

Our tendency to assume that big events have big causes.

Example of Proportionality Bias

Some believed that because Princess Diana was such a world-known, prominent public figure that she died as the result of conspiracy within the government and British Royal Family rather than a car accident caused by a speeding driver (who had been drinking) losing control of the vehicle.