Heuristics, Biases, and Fallacies: Definitions and Key Differences
People often use the terms heuristics, cognitive biases, and logical fallacies interchangeably. While they can be connected, they don’t mean the same thing: heuristics are mental shortcuts, cognitive biases are systematic errors in thinking, and logical fallacies are flawed arguments. In this post, I’ll define each term with examples and explain their relationship.
What are heuristics?
A heuristic is a shortcut your mind uses to make decisions with less effort. Heuristics aren’t necessarily bad—in fact, they’re often useful. In many situations, it would be impractical to weigh every option and do a full cost-benefit analysis. Heuristics reduce mental effort and make decisions faster. However, that efficiency can come at the expense of accuracy. In some contexts, heuristics mislead us and lead to poor decision-making.
Example: Familiarity heuristic
Imagine you’re buying toilet paper. You probably don’t want to compare every brand’s softness, strength, price per sheet, and long-term value. Instead, you might pick the brand you recognize—the one you’ve bought before. That’s the familiarity heuristic: treating what’s familiar as safer or better. This often works fine because familiar products can be reliable. But it can also keep you from noticing better options.
Example: Satisficing heuristic
Satisficing means setting a clear “good enough” standard and choosing the first option that meets it. If you need to buy a new mouse and your requirements are clear, satisficing can be a rational approach. You may not end up with the absolute best mouse for you, but you’ll get a perfectly workable one without spending hours comparing tiny differences. In low-stakes decisions, the time and mental energy required to optimize can cost more than the improvement you’d gain from choosing the best.
Heuristics often replace hard questions with easier ones:
- Hard question: “Which choice is best?”
- Easier questions: “Which choice is familiar?” “Which choice is good enough?”
What are cognitive biases?
A cognitive bias is a predictable distortion in how we perceive information, interpret evidence, estimate likelihood, or make choices. “Bias” here doesn’t mean prejudice—it means a systematic deviation from accurate judgment (though some cognitive biases can contribute to prejudice).
Example: Confirmation bias
Confirmation bias is the tendency to notice, search for, or interpret evidence in a way that supports what you already believe, while giving less attention to evidence that challenges it.
Example: Self-serving bias
Self-serving bias is the tendency to explain successes as due to your own ability or effort (“I earned this”) while explaining failures as due to external factors (“the test was unfair,” “I had bad luck”). This bias protects self-image and reduces discomfort after a negative outcome.
Heuristics vs cognitive biases
Heuristics and biases are related, but they’re not the same thing. Heuristics are mental shortcuts, whereas cognitive biases are systematic distortions in judgment.
Heuristics can (but don’t always) lead to biases. Many heuristics are reasonable and useful in everyday life. They’re most likely to produce biased judgments when we’re under time pressure, distracted, emotional, or relying on incomplete information. For example, we saw that one heuristic is using familiarity as an indication that something is good. That can lead to bias when it systematically skews judgments—for instance, treating familiar risks as safer than unfamiliar ones (even when they statistically aren’t), or in hiring, where a familiar accent, name, or school can make a candidate seem like a better fit than they actually are.
Not every bias comes from a heuristic. Cognitive biases can arise from multiple sources. Some are driven by motivation (wanting a particular conclusion), emotion (fear, disgust, excitement), or selective attention and memory.
Example: Availability
After recent news coverage of a plane crash, flying may feel more dangerous than usual even though the risk hasn’t changed. This happens because the example is vivid, recent in memory, and easy to recall. This tendency to use what comes to mind quickly when making a judgment (for example, about likelihood) is called the availability heuristic.
This heuristic can be helpful when ease of recall represents what you’re likely to encounter (for example, quickly remembering common hazards in your routine environment). But it can produce a cognitive bias when judgments of risk are shaped more by what comes to mind easily than by base rates.
What are logical fallacies?
A logical fallacy is a flaw in reasoning. In other words, logical fallacies are bad arguments.
Example: Ad hominem
You commit the ad hominem fallacy when you attack the person making an argument rather than the argument itself. For example, if someone argues that people should have at least one exercise recovery day per week, and someone responds, “You are wrong because you’re not fit,” that’s the ad hominem fallacy because the rebuttal targets the person, not the claim.
Note: If someone’s character is directly relevant to the claim, that’s different. For example, if someone argues they should be trusted, and you point out they’ve acted in an untrustworthy manner in the past, that’s not a fallacy.
Example: Straw man
The straw man fallacy happens when someone misrepresents another person’s position and then argues against that distorted version instead of the original claim. For example, imagine someone argues for better privacy laws. In response, another person starts criticizing the harms of shutting down the internet. That response is aimed at a straw man since the original argument wasn’t that the internet should be shut down.
Where logical fallacies show up
Logical fallacies can show up in debates, persuasive writing, advertising, and everyday conversations. They can also show up privately in your internal monologue when you’re trying to think something through.
Fallacies can be used intentionally or unintentionally. Sometimes they’re used deliberately as a debate or persuasion strategy. Other times they happen unintentionally, often as a result of cognitive biases.
Cognitive biases vs logical fallacies
A logical fallacy is a reasoning mistake in which the reasons don’t support the conclusion. A cognitive bias, by contrast, is a predictable distortion in judgment that can shape what feels convincing or what information we notice in the first place. Biases can contribute to fallacious reasoning, but fallacies aren’t always driven by bias; they’re sometimes used deliberately as tactics to make a position seem stronger or to “win” a dispute.
Example: Sunk costs
When people talk about the “sunk cost fallacy,” they’re often actually describing a bias. The sunk cost bias is the urge to continue with something simply because you’ve already invested in it and you don’t want that time or money to feel wasted—even when switching course would likely lead to better outcomes.
It is a logical fallacy when you turn that feeling into an argument. Imagine you’re on a team at work. The team wants to move to a more promising project, but because you’ve invested a lot in the current one, you argue: “We can’t quit now because if we do, then all that time and effort will have been for nothing.” Arguing that past costs are a reason to continue, even though they can’t be recovered, is the sunk cost fallacy.
The sunk cost bias can plausibly be supported by simple heuristics like “don’t waste resources,” “finish what you started,” or “sticking with a plan is better than quitting.” To mitigate the bias, focus on what matters now: whether continuing improves expected outcomes from this point forward given the current situation.
Example: Risk perception
We’ve already seen that biased risk perception can arise when availability or familiarity cues override statistical information. This can lead to logical fallacies such as arguing that a medication is unsafe because someone had a serious side effect after taking it. The fact that an event occurred doesn’t tell you how likely it is.
Summary
- Heuristics are mental shortcuts we use to make quick decisions.
- Those shortcuts can produce cognitive biases, especially under certain conditions (stress, time pressure, strong emotions).
- Biases can lead to logical fallacies when we justify a biased feeling or decision with a flawed argument.
- Not all biases are produced by heuristics.
- Not all fallacies are caused by cognitive biases.
