Unit 5: Fallacies
Now that you have studied the necessary structure of a good argument and can represent its structure visually, you might think it would be simple to pick out bad arguments. However, identifying bad arguments can be very tricky in practice. Very often, what at first appears to be ironclad reasoning turns out to contain one or more subtle errors.
Fortunately, there are many easily identifiable fallacies (mistakes of reasoning) that you can learn to recognize by their structure or content. In this unit, you will learn about the nature of fallacies, look at a couple of different ways of classifying them, and spend some time dealing with the most common fallacies in detail.
Completing this unit should take you approximately 3 hours.
Upon successful completion of this unit, you will be able to:
- explain fallacies of inconsistency, irrelevance, insufficiency, and inappropriate presumption;
- identify common fallacies, including the straw man, gambler's fallacy, begging the question, red herring, ad hominem, appeal to ignorance, appeal to people, complex question, loaded question, and non-sequitur; and
- describe the nature of a cognitive bias and identify examples of cognitive bias.
5.1: Introduction to Fallacies
Read this tutorial, which introduces the notion of fallacious reasoning. Fallacies are arguments that are frequently accepted as valid but contain subtle reasoning errors. It is important to know how to catch fallacies.
5.2: Types of Fallacies
Read this section to learn the difference between formal and informal fallacies and learn two key formal fallacies that look like good logic but are not: denying the antecedent and affirming the consequent. There is a popular joke among philosophers about Descartes (the French philosopher who famously wrote, "I think, therefore I am") walking into a bar and, when the bartender asks if he'd like a drink, replying "I think not" and vanishing in a puff. While delightful to share among your philosopher friends, this joke actually falls prey to one of these fallacies – see if you can tell why.
Read this tutorial, which defines the most common fallacies. This list narrows down some of the fallacies in the previous text and is enough to get us started. We will look at a wider sample of fallacies later in this course. For now, focus on defining each fallacy and identifying the differences between the fallacies on the list.
Read these sections to review three important fallacies you probably come across without realizing it: false dichotomy, causal slippery slope fallacy, and appeal to authority.
All three of these fallacies can be disguised as something that looks logical, but these readings will help you identify when that is not the case.
Read these tutorials, which introduce four major classifications of fallacies. Although there are many possible ways of categorizing fallacies, the four major groups discussed in these tutorials are fairly standard.
5.3: Ten Common Fallacies in Detail
5.3.1: Straw Man Fallacy
You may have heard criticisms of a "straw man" argument before and not known what that meant. This section walks you through a straw man argument and gives examples. After reading this section, try to come up with a few examples of straw man arguments, and look for straw man fallacies in your own life.
Watch this video, which explains a fallacy commonly known as the straw man fallacy. After watching this video, you should be able to define the fallacy and identify examples of the fallacy.
5.3.2: Gambler's Fallacy
Watch this video, which explains a fallacy commonly known as the gambler's fallacy. After watching this video, you should be able to define the fallacy and identify examples of the fallacy.
Read this introduction to the gambler's fallacy and the example of how it works.
5.3.3: Begging the Question
Read this section on the fallacy of "begging the question". When we formalize the examples in the premise, they are not substantively different from the conclusion. Look out for "question begging" arguments in your life.
5.3.4: Red Herring
Read this article to learn about the red herring fallacy. If you think bringing up colorful fish sounds out of place when discussing logic, then you're right! The red herring fallacy operates by bringing up irrelevant information. Often when we have arguments in our lives, though, people throw in "red herrings".
5.3.5: Ad Hominem (Against the Person)
You have doubtless heard ad hominem attacks before – though you may not have known they were an informal fallacy. Read this section on the ad hominem fallacy for a definition and examples of these attacks. After reading, you should be able to identify ad hominem attacks when you encounter them.
5.3.6: Ad Ignorantium (Appeal to Ignorance)
Read this brief description of the "ad ignorantium" (or "appeal to ignorance") fallacy. This common fallacy insists on placing the burden of proof on whatever side opposes it.
5.3.7: Ad Populum (Appeal to the People)
Read this article for a quick explanation and examples of the logical fallacy ad populum, or "appeal to the people". This fallacy relies on our social inclinations and is popularly seen in advertising. Despite the effectiveness of these kinds of appeals, they nonetheless are not logical arguments.
5.3.8: Complex Question (Double-Barreled Question)
Read this article, which defines the double-barreled question fallacy and identifies examples of it.
5.3.9: Loaded Question
Read this article, which defines the loaded question fallacy and identifies examples of it.
5.3.10: Non Sequitur (It Does Not Follow)
Read this article, which defines the non sequitur fallacy and identifies examples of it.
5.3.11: Review of Fallacies
- Make forum posts: 1
Consider the passages below. If the passage contains an argument, identify the premises and main conclusion. For each passage, assess whether it contains a fallacy. If it does, identify the fallacy and explain why you made your assessment.
- God exists because many people who believe in God go on to have healthy, happy, and meaningful lives.
- Bertrand Russell (1872–1970), the British philosopher, said that objective morality is possible without God. Russell was an atheist, and we all know that he slept around and seduced young girls and was nasty to many people.
- Do you want four more years of this person in political office? Vote for me, Candidate X.
Share your thoughts on the discussion forum. Make sure to review and respond to other students' posts, as well.
5.4: Cognitive Biases
Read this tutorial, which describes some examples of cognitive biases. These biases are ways of thinking that lead us to make poor inferences. Being able to identify cognitive biases helps us to improve our reasoning and helps us to assess other people's reasoning.
Watch this video to learn about availability, representativeness, and confirmation biases. Note that there are many other cognitive biases, including anchoring bias, availability heuristic bias, bandwagon bias, choice supportive bias, ostrich bias, outcome bias, overconfidence, placebo bias, survivorship bias, selective perception bias, and blind spot bias. Try to identify some examples of cognitive biases in your life.