Informal Fallacies

An informal fallacy occurs because of an error in reasoning. Unlike formal fallacies which are identified through examining the structure of the argument, informal fallacies are identified through analysis of the content of the premises. In this group of fallacies, the premises fail to provide adequate reasons for believing the truth of the conclusion. There are numerous different types of informal fallacies. In the following, we consider some of the more common types.

accident (sweeping generalization)

A fallacy by accident occurs when a generally true statement is applied to a specific case that is somehow unusual or exceptional. The fallacy looks like this:

Xs are normally Ys. Z is an (ab- normal) X. Therefore, Z is an Y.

Let’s look at a specific example to see how this fallacy can easily occur:

Dogs are good pets.
Coyotes are dogs.
Therefore, coyotes are good pets.

coyoteThe fallacy here should be clear. I love dogs and coyotes, but I don’t know that I would want a coyote for a pet. The fallacy in this case could be easily fixed with the use of a simple qualifier such as the word “some.” If we changed the first premise to read “Some dogs make good pets,” then we can see how even if the second premise is true it doesn’t automatically lead to the stated conclusion. The basic problem here is that a sometimes true statement is assumed to be universally true.

I do personal attacks only on people who specialize in personal attacks. – Al Franken

genetic fallacy (ad hominem)

If we examine this exchange we can see that Bill’s arguments are sound and supported by what appears to be good evidence. However, Jane ignores these and focuses on Bill’s supposed character – he’s a big jerk. The fallacy happens when we connect the truth of a proposition to the person asserting it.

The ad hominem fallacy occurs when we shift our focus from the premises and conclusions of the argument and focus instead on the individual making the argument. An easy way to remember this fallacy is to think of it as the personal attack fallacy. It is the weak form of arguing that many of us employed on our elementary school playgrounds such as this exchange:

Bill: I think we should go back to class now.

Jane: I don’t think we need to worry about it.

Bill: Well, the bell rang a few minutes ago. We’re going to be late.

Jane: Well, you’re a big jerk and don’t know anything, so we don’t have to go back to class.

If we examine this exchange we can see that Bill’s arguments are sound and supported by what appears to be good evidence. However, Jane ignores these and focuses on Bill’s supposed character – he’s a big jerk. The fallacy happens when we connect the truth of a proposition to the person asserting it.

Let’s consider a more serious example that we see in many political campaigns. We can map out the fallacy as follows:

My opponent has trait X. Therefore, she is not qualified to do the job.

The focus here is on the individual’s trait, even when the trait in question has nothing to do with the job. We saw this fallacy in play in the early days of the 2012 U.S. presidential campaign:

We will never get out of debt if we allow a Democrat to remain as president.

The focus here has nothing to do with any individual candidate’s skills, experience, or abilities. The focus is solely on their political affiliation.

There is no greater impediment to the advancement of knowledge than the ambiguity of words. – Thomas Reid

ambiguity (equivocation)

Fallacies caused by ambiguity occur, not surprisingly, when some ambiguous term is used in the argument. An ambiguous term is one that has more than one meaning. The structure of the argument may be clear, and there may be solid evidence supporting the propositions. The problem arises from having nothing solid on which to base our conclusion. We saw this fallacy in play during the Clinton/Lewinsky investigations. If you recall, when questioned about his relationship with Monica Lewinsky, President Clinton responded that he never had “sexual relations” with that woman. The phrase “sexual relations” can include a whole range of sexual behaviors.

Soldiers exiting home in IraqLet’s look at a more recent example:

We won’t be safe until we win the war on terrorism.

Can you spot the ambiguity? Actually there are two: safe and terrorism. What is safe to one person is much less so to another. Likewise, behaviors that appear terrorist-like to one person are simply impassioned acts to another.

An appeal to the reason of the people has never been known to fail in the long run. – James Russell Lowell

fallacies of appeal

This type of fallacy is actually a group of fallacies. At its most basic, the truth of the argument rests on reference to some outside source or force. We will consider four of the most popular appeal fallacies – appeals to authority, emotion, ignorance, and pity.

appeal to authority (ad vericundiam)

When we appeal to authority we claim the truth of a proposition is guaranteed because of the opinion of a famous person. Appeals to authority look like this:

Authority figure X says Y. Therefore, Y is true.

Doctor in surgical maskWe see this fallacy in play regularly in commercials or other advertisements featuring a doctor, lawyer, or other professional. Think about, for example, ads for the latest weight loss supplement. A doctor will discuss the science of the supplement. At times she will mention that she used the supplement and successfully lost weight. Even though we do learn something about the specifics of the supplement, the focus is on the doctor and her implied authoritative knowledge. We are to infer that the supplement will work because the doctor says it will work.

The fallacy in this type of reasoning occurs when we confuse the truth of the proposition with the person stating it. Instead of considering the strength of the argument and any evidence associated with it, we focus solely on the individual.

It can be easy to fall into the trap of this fallacy. For many of your speeches, you will be asked to research the issue at hand and present supporting evidence. This is a prime place for the fallacy to occur. While it is important to support your arguments with outside research, it is also important to critically evaluate all aspects of the information. Remember the example of Shonda’s speech that opened this chapter? Her blind reliance on the research of Dr. Gray is an example of the appeal to authority fallacy.

Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory. – Leonardo da Vinci

appeal to emotion

This fallacy occurs with the use of highly emotive or charged language. The force of the fallacy lies in its ability to motivate the audience to accept the truth of the proposition based solely on their visceral response to the words used. In a sense, the audience is manipulated or forced into accepting the truth of the stated conclusions. Consider the following example:

Any campus member who thinks clearly should agree that Dr. Lenick is a flaming, radical, feminist, liberal. Dr. Lenick has made it clear she believes that equal rights should be granted to everyone without regard to the traditions and history of this campus or this country. Therefore, Dr. Lenick is a bad teacher and should be fired immediately.

The thrust of this argument revolves around two interrelated components – Dr. Lenick’s advocacy of equal rights for all and her alleged disregard for tradition and history. The emotional appeal rests in the phrase “flaming, radical, feminist, liberal” – words that indicate ideological beliefs, usually beliefs that are strongly held by both sides. Additionally, hot button words like these tend to evoke a visceral response rather than a logical, reasoned response.

The highest form of ignorance is when you reject something you don’t know anything about. – Wayne Dyer

appeal to Ignorance (argumentum ad ignorantiam)

When we appeal to ignorance, we argue that the proposition must be accepted unless someone can prove otherwise. The argument rests not on any evidence but on a lack of evidence. We are to believe the truth of the argument because no one has disproven it. Let’s look at an example to see how appeals to ignorance can develop:

People have been seeing ghosts for hundreds of years. No one has been able to prove definitively that ghosts don’t exist. Therefore, ghosts are real.

Though rather simplistic, this example makes clear the thrust of this fallacy. The focus is not on supporting evidence, but on a blatant lack of evidence. While ghosts may exist, we don’t know for sure they do – or don’t for that matter. As such, we could also argue that because we can’t prove that ghosts are real they must not exist.

appeal to pity (argumentium ad misericordium)

Appeals to pity are another form of pulling on the emotions of the audience. In the appeal to pity, the argument attempts to win acceptance by pointing out the unfortunate consequences that will fall upon the speaker. In effect, the goal is to make us feel sorry for the speaker and ignore contradictory evidence. This form of fallacy is used often by students. Consider this message a professor recently received at the end of the semester:

basketball hoopI know I have not done all the work for the semester and have been absent a lot. However, I am the key point guard for the basketball team. If I get any grade lower than a C, I will not be able to play basketball next semester. If I don’t play, the team will lose. Will you please make sure that you give me at least a C for my final grade?

The student here acknowledges he does not deserve a grade of C or higher. He has missed assignments, failed the midterm, and accrued a number of absences. His argument asks the professor to ignore these facts, though, and focus on the fact that without him the team would lose. In other words, he hopes the professor will feel sorry for him and ignore the evidence.

begging the question (petitio principii)

A begging the question fallacy is a form of circular reasoning that occurs when the conclusion of the argument is used as one of the premises of the argument. Arguments composed in this way will only be considered sound or strong by those who already accept their conclusion.

Dilbert: And we know mass creates gravity because more dense planets have more gravity.

Dogbert: How do we know which planets are more dense?

Dilbert: They have more gravity.

To see how begging the question develops as a fallacy, let’s turn to standard arguments in the abortion debate. One of the common arguments made by those who oppose legalized abortion is the following:

Murder is morally wrong. Abortion is murder. Therefore, abortion is morally wrong.

Most people would agree with the first premise that murder is morally wrong. The problem, then rests in the second premise. Not all individuals would agree that abortion is murder. However, as presented, the premise creates a presumption it is valid in all cases.

Those who advocate for legalized abortion are not immune from this fallacy. One of their standard arguments is:

The Constitution guarantees Americans the right to control their bodies.
Abortion is a choice affecting women’s bodies.

Therefore, abortion is a constitutional right.

Like the previous example, the second premise generates a potential stopping point. While the choice to have or not have an abortion does clearly impact a woman’s body, many individuals would argue this impact is not a deciding issue.

black-or-white Fallacy (bifurcation)

This fallacy is also known as an Either/or fallacy or False Dichotomy. The thrust of the fallacy occurs when we are only given the choice between two possible alternatives, when in fact more than two exist.
Bifurcated manReturning to the abortion debates, we can see a form of this fallacy in play by simply looking at the way each side refers to itself. Those who oppose legalized abortion are Pro-Life. The implication here is that if you are for abortion then you are against life. The fallacy in this case is easy to figure out – there are many facets of life, not just abortion. Those who favor legalized abortion are Pro-Choice. The implication here is that if you are against abortion, then you are against choices. Again, the reasoning is faulty.

There is no black-and-white situation. It’s all part of life. Highs, lows, middles. – Van Morrison

Let’s look at another hot button topic to see how this fallacy develops in action. In recent years many family advocacy groups have argued that, what they call, the “liberal media” has caused the rapid moral decline of America. They usually ask questions like: Do you support families or moral depravity? This question ignores the whole range of choices between the two extremes.


This fallacy occurs when we assume that if all the parts have a given quality, then the whole of the parts will have it as well. We jump to a conclusion without concrete evidence. We see this fallacy at work in the following example:

All of the basketball team’s players are fast runners, high jumpers, and winners. Therefore, the team is a winner.

The problem here is the individuals must work together to make the team a winner. This might very well happen, but it might not.

To make this fallacy more clear, let’s look at a humorous, though not so appetizing example:

I like smoothies for breakfast because I can drink them on the run. My favorite breakfast foods are scrambled eggs, fresh fruit, bagels with cream cheese, soy sausage links, cottage cheese, oatmeal, cold pizza, and triple espressos. Therefore, I would like a breakfast smoothie made of scrambled eggs, fresh fruit, bagels with cream cheese, soy sausage links, cottage cheese, oatmeal, cold pizza, and triple espressos.

If you’re not feeling too nauseated to keep reading, you should be able to see the composition fallacy here. While each of these breakfast items may be appetizing individually, they become much less so when dropped into a blender and pureed together.


The opposite of the composition fallacy, a division fallacy occurs when we think the parts of the whole contain the same quality as the whole. Let’s turn to another food-based example to see how this fallacy occurs:

Blueberry muffins taste good. Therefore, the individual ingredients comprising blueberry muffins also taste good.

blueberry muffinOn the surface, this argument may not appear to be problematic. However, think about the individual ingredients: blueberries, raw eggs, flour, sugar, salt, baking soda, oil, and vanilla. Of these, blueberries are the only items that generally taste good on their own. I don’t know about you, but sitting down to a bowl of baking soda doesn’t sound too appetizing.

Here’s one more example to make the fallacy clearer:

Women in general make less money than men. Therefore, Brenda Barnes, CEO of the Sara Lee company, makes less money than the male delivery drivers who work for the company.

Common sense will tell you the CEO of a company makes more money than the hourly delivery drivers. Additionally, a few quick minutes of research will confirm this inference.

false cause (non causa, pro causa)

Sometimes called a Questionable Cause fallacy, this occurs when there exists a flawed causal connection between events. The fallacy is not just a bad inference about connection between cause and effect, but one that violates the cannons of reasoning about causation. We see two primary types of this fallacy.
sick womanAccidental or coincidental connection occurs when we assume a connection where one might or might not exist. We say event C caused event E when we have no clear proof. Here’s an example:

Yesterday Jen went out in the rain and got soaked. The next day she was in bed with the flu. Therefore, the rain caused her to get sick.

Most of us probably grew up hearing statements like this without ever realizing we were being exposed to a logical fallacy in action. Flu is caused by exposure to a virus, not to bad weather.

The other type of causal fallacy occurs with a general causation between types of events. For example, we know that drinking excessive amounts of alcohol leads to alcoholism and cirrhosis of the liver. However, not every individual who drinks excessively develops either of these diseases. In other words, there is a possibility the disease will occur as a result of excessive drinking, but it is not an absolute.

red herring (irrelevant thesis)

This fallacy occurs when we introduce an irrelevant issue into the argument. The phrase “red herring” comes from the supposed fox hunting practice of dragging a dried smoke herring across the trail so as to throw off the hound from the scent. In logical reasoning, the red herring fallacy works in much the same way. No, this doesn’t mean you make the argument while smelling like an old fish. What it does mean is that we attempt to distract the audience by introducing some irrelevant point, such as this:

Each year thousands of people die in car accident across the country. Why should we worry about endangered animals?

This argument is trying to get us to focus on dead people instead of animals. While car accidents and the deaths resulting from them are a serious issue, this fact does not lessen the importance of worrying about endangered animals. The two issues are not equated with each other.

Political campaigns are a fertile ground for growing red herring fallacies. If you think back to the 2004 Presidential campaign you will find a number of red herrings. For example, at one point we were inundated with ads reminding us that John Kerry’s wife was heir to the Heinz ketchup fortune. The implication was that by extension John Kerry was a rich elitist incapable of understanding the plight of working class and middle class individuals.

slippery slope

Slippery slope

This fallacy occurs when we assume one action will initiate a chain of events culminating in an undesirable event later. It makes it seem like the final event, the bottom of the slope, is an inevitability. Arguments falling prey to the slippery slope fallacy ignore the fact there are probably a number of other things that can happen between the initial event and the bottom of the slope.

We hear examples of the slippery slope fallacy all around us:

If we teach sex education in school, then students will have more sex. If students have more sex, we will have a rash of unplanned pregnancies and sexually transmitted diseases. Students will be forced to drop out of school and will never have the chance to succeed in life.

Clearly, just learning about sex doesn’t automatically mean that you will engage in sex. Even more unlikely is the fact that merely learning about sex will force you to drop out of school.


This fallacy occurs when the actual argument appears to be refuted, but in reality a related point is addressed. The individual using a strawman argument will appear to be refuting the original point made but will actually be arguing a point not made in the original. The best strawman arguments will argue the new point to a conclusion that appears solid; however, because their point is not the original point, it is still a fallacy.

Examples of the strawman fallacy are everywhere and can appear to be quite persuasive:

President Obama cannot truly have American interests in mind because he’s not truly American but Muslim.

Statements similar to this were quite prevalent during the 2008 Presidential election and still appear on occasion. The assumption here is that if a person follows Islam and identifies as Muslim they clearly can’t be American or interested in America. While there are many potential flaws in this argument as presented, for our purpose the most obvious is that there are many Americans who are Muslim and who are quite interested and concerned about America.

false analogy

When we use analogies in our reasoning, we are comparing things. A fallacy of weak analogy occurs when there exists a poor connection between examples. Structurally, the fallacy looks like this:Comparing applies and oranges

A and B are similar.
A has characteristic X. Therefore, B has characteristic X.

This fallacy often occurs when we try to compare two things that on the surface appear similar. For example:

Humans and animals are both living, breathing beings. Humans have civil rights. Therefore, animals have civil rights.

The problem in this argument is that while humans and animals are alike in their living and breathing status, there are numerous other ways they differ. We commit a fallacy when we infer that based on this initial similarity, they are similar in all other ways as well.

The other day while looking at houses, I heard another version of this argument from a real estate agent. The house I was looking at was an older house needing some TLC. I asked how old the roof was and the real estate agent responded:

I don’t know for sure, but it’s either 10 or 20 years old. You know, though, I put a roof on a house similar to this when I was younger and we haven’t had to worry about it. It’s been over 20 years now.

Ignoring for the moment that there’s a big difference between a 10-year-old roof and a 20-year-old roof, the real estate agent mistakenly assumes that his roof and the roof of the TLC house are the same. They both provide a covering for the home, but that’s about where their similarities end.