Fallacies & General Logic


What is Logic?

The term "logic" came from the Greek word logos, which is sometimes translated as sentence, discourse, reason, rule, ratio or word. Of course, these translations are not enough to help us understand the more specialized meaning of "logic" as it is used today. So what is logic? Briefly speaking, we might define logic as the study of the principles of correct reasoning. This is a rough definition, because how logic should be properly defined is actually quite a controversial matter.

One thing you should note about this definition is that logic is concerned with the principles of correct reasoning. Studying the correct principles of reasoning is not the same as studying the psychology of reasoning. Logic is the former discipline, and it tells us how we ought to reason if we want to reason correctly. Whether people actually follow these rules of correct reasoning is an empirical matter, something that is not the concern of logic. The psychology of reasoning, on the other hand, is an empirical science. It tells us about the actual reasoning habits of people, including their mistakes. A psychologist studying reasoning might be interested in how people's ability to reason varies with age. But such empirical facts are of no concern to the logician.

(From: The Critical Thinking Web, Copyright Joe Lau & Jonathan Chan)

"In Greek and Roman antiquity, discussions of some elements of logic and a focus on methods of inference can be traced back to the late 5th century BCE. The Sophists, and later Plato (early 4th c.) displayed an interest in sentence analysis, truth, and fallacies.... Logic as a fully systematic discipline begins with Aristotle, who systematized much of the logical inquiry of his predecessors." (From Stanford Encyclopedia of Philosophy)

Ad Hominem Attack (John Oliver/Fox News)

Logic & Argument:

What is logic?
Most academic writing tasks require you to make an argument—that is, to present reasons for a particular claim or interpretation you are putting forward. You may have been told that you need to make your arguments more logical or stronger. And you may have worried that you simply aren't a logical person or wondered what it means for an argument to be strong. Learning to make the best arguments you can is an ongoing process, but it isn't impossible: “Being logical” is something anyone can do, with practice. Each argument you make is composed of premises (this is a term for statements that express your reasons or evidence) that are arranged in the right way to support your conclusion (the main claim or interpretation you are offering). You can make your arguments stronger by
  1. using good premises (ones you have good reason to believe are both true and relevant to the issue at hand),
  2. making sure your premises provide good support for your conclusion (and not some other conclusion, or no conclusion at all),
  3. checking that you have addressed the most important or relevant aspects of the issue (that is, that your premises and conclusion focus on what is really important to the issue you're arguing about), and
  4. not making claims that are so strong or sweeping that you can't really support them.
This handout describes some ways in which arguments fail to do the things listed above; these failings are called fallacies. If you're having trouble developing your argument, often a fallacy is part of the problem.
It is particularly easy to slip up and commit a fallacy when you have strong feelings about your topic—if a conclusion seems obvious to you, you're more likely to just assume that it is true and to be careless with your evidence. Weak reasoning can happen in pretty much any kind of argument, however.

Here is a link to further explanation of Logical Fallacies.

mental5-4.gifKOS Series on Logic

"The skills of clear thinking & sound reasoning remain the best counters to the otherwise persuasive power of prejudice & propaganda. (Skill in the art of active persuasion, rhetoric, helps against them as well — but it works best when well-informed by logic.)" by Brown Thrasher at the Daily Kos

Informal Fallacies, Part I
Informal Fallacies, Part II
Informal Fallacies, Part III
Informal Fallacies, Part IV
Informal Fallacies, Part V
Informal Fallacies, Part VI

What are fallacies?

online resource
Recognizing Fallacies
Critical Thinking Series: Project of Australian Government, James Hutson
  1. Valuable Argument, Part I
  2. Broken Logic, Part II
  3. The Man Who Was, Part III
  4. Getting Personal, Part IV
  5. The Gamblers Fallacy, Part V
  6. A Precautionary Tale, Part VI


Fallacies are defects that weaken arguments. By learning to look for them in your own and others' writing, you can strengthen your ability to evaluate the arguments you make, read, and hear. It is important to realize two things about fallacies: First, fallacious arguments are very, very common and can be quite persuasive, at least to the casual reader or listener. You can find dozens of examples of fallacious reasoning in newspapers, advertisements, and other sources. Second, it is sometimes hard to evaluate whether an argument is fallacious. An argument might be very weak, somewhat weak, somewhat strong, or very strong. An argument that has several stages or parts might have some strong sections and some weak ones. The goal of identifying fallacies, is not to teach you how to label arguments as fallacious or fallacy-free, but to help you look critically at your own arguments and move them away from the "weak" and toward the "strong" end of the continuum.

Here are some general tips for finding fallacies in your own arguments:
  • Pretend you disagree with the conclusion you're defending. What parts of the argument would now seem fishy to you? What parts would seem easiest to attack? Give special attention to strengthening those parts.
  • List your main points; under each one, list the evidence you have for it. Seeing your claims and evidence laid out this way may make you realize that you have no good evidence for a particular claim, or it may help you look more critically at the evidence you're using.
  • Learn which types of fallacies you're especially prone to, and be careful to check for them in your work. Some writers make lots of appeals to authority; others are more likely to rely on weak analogies or set up straw men. Read over some of your old papers to see if there's a particular kind of fallacy you need to watch out for.
  • Be aware that broad claims need more proof than narrow ones. Claims that use sweeping words like "all," "no," "none," "every," "always," "never," "no one," and "everyone" are sometimes appropriate—but they require a lot more proof than less-sweeping claims that use words like "some," "many," "few," "sometimes," "usually," and so forth.
  • Double check your characterizations of others, especially your opponents, to be sure they are accurate and fair


Beatles: Logical Fallacies
Cartoon: Logical Fallacies
In Fact: Logical Fallacies (Part 1)
In Fact: Logical Fallacies (Part 2)
In Fact: Logical Fallacies (Part 3)
Professor Flagbag/Logical Fallacies, Part 1
Professor Flagbag/Logical Fallacies, Part 2

Ad Hominem Fallacy

Rachel Maddow & Bill O'Riley

Another example of Ad Hominem

Tammy-Duckworth.jpgThe 2012 election of Iraq War veteran Tammy Duckworth to the US House of Representatives

An example of an Ad Hominem attack from the "real world"

2013: Fallacies in the News
Monty Python: She's a witch
Annenberg Classroom Examples