Bias or Fallacy?

A clear understanding of the terms being used is one of the foundations of critical thinking, so let’s be sure we know the difference between a cognitive bias and a logical fallacy. Both things raise red flags because both things cause problems, but it’s important to keep track of how the problem gets generated. A cognitive bias is a problem with the way we habitually think; a logical fallacy is a failure in reasoning. Understanding the difference helps us understand possible causes or motivations for unhelpful thinking.


A cognitive bias arises from ingrained thinking patterns, sometimes called Type One thinking. We tend to see the world through the filter of our own experiences and preferences, and those can lead us to make use of certain mental short cuts or heuristics. Relying on heuristics is a two-edged sword: heuristics can be surprisingly accurate, but they can also lead to big errors–especially when we try to hold on to our personal preferences in spite of disconfirming evidence.

When we see things that do not fit with our preconceptions about the world, our first impulse is to want to change the world to fit our preconceptions rather than pursue an examination of the accuracy of our perceptions of the world. Confirmation Bias is a good example–our tendency to favor information that confirms our point of view and to ignore contrary information. And so a cognitive bias can be thought of as a kind of systems error; it is a habitual or automatic way of thinking that can save time but must be double-checked.

Fallacies, on the other hand, have less to do with structural errors in thinking and usually require a careful look at content. Fallacies generally occur in three forms: fallacies of relevance, fallacies of ambiguity, and fallacies of presumption. Fallacies of relevance occur when information is brought into an argument that has no bearing on the issue. The introduction of irrelevant information can be a tactic used to distract or can be the result of sloppy thinking. For example, a personal attack (the ad hominem fallacy) is not relevant in most cases because it is unrelated to the issue at hand–we discuss claims, not personal qualities. To claim someone’s argument is wrong because the person making the argument has a negative personality characteristic is wrong-headed and unfair. We must stick to the issue.

Fallacies of ambiguity are problems that arise from the use of unclear terms or shifting definitions of key terms. The fallacy known as Equivocation is an example of this. It occurs when a key term in an argument is redefined:

All trees have bark.

Dogs bark.

Therefore, dogs are trees.

The equivocated term here is ‘bark.’ We have to use words in an argument consistently without shifting meanings or interpretations. The material covering tree trunks and the sound a dog makes are two very different meanings.

Fallacies of presumption occur in statements that pass off an idea as true without showing support for that conclusion. Loaded questions are fallacies of this type. “When did you stop beating your wife?” is a question that presumes you were indeed beating your wife, but that act has not yet been shown to be true. The either/or fallacy or false dilemma is another example. This fallacy occurs when we are pushed to make a choice that includes only two options when in reality there may be many more. “My way or the highway,” “Either you’re with me or you’re against me,” “Do you want to go to college or do you want to dig ditches for the rest of your life” are arguments with presumptions that haven’t been shown to be true and that restrict our decision-making to one of only two possibilities when there may well be many more.

We are all subject to cognitive bias because of our habitual ways of thinking. Fallcies are more often the result of an active attempt at manipulation or just plain sloppy reasoning. In future posts, we’ll look at specific biases and fallacies and talk about guarding against them.

Author: Craig Butcher

Craig Butcher is an award-winning educator who has taught critical thinking skills for more than two decades. In addition, He has worked on Capitol Hill as a congressional aide and has been a top-rated broadcaster.