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Logical Fallacies

Now that we have examined the components of logic that make up an argument, let’’s define some logical fallacies. Fallacies in an argument are elements of faulty reasoning that weaken the argument and may even make it invalid.



Contradiction is the most glaring type of fallacy. It is committed when two opposing statements are simultaneously asserted. For example, saying ““it is raining and it is not raining”” is a contradiction. Typically, however, the writer obscures the contradiction to the point that the argument can be quite compelling. Take, for instance, the following argument:


““We cannot know anything, because we intuitively realize that our thoughts are unreliable.””


This argument has an air of reason to it. But intuitively realize means ““to know.”” Thus the writer is in essence saying that we know that we don’’t know anything. This is self-contradictory.


Equivocation is the use of a word in more than one sense during an argument. This technique is often used by politicians to leave themselves an ““out.”” If someone objects to a particular statement, the politician can simply claim the other meaning.


Individual rights must be championed by the government. It is right for one to believe in God. So government should promote the belief in God.


In this argument, right is used ambiguously. In the first sentence, it is used in the sense of a privilege, whereas in the second sentence right is used to mean proper or moral. The questionable conclusion is possible only if the arguer is allowed to play with the meaning of the critical word right.

Circular Reasoning

Circular reasoning involves assuming as a premise that which you are trying to prove. Intuitively, it may seem that no one would fall for such an argument. However, the conclusion may appear to state something additional, or the argument may be so long that the reader may forget that the conclusion was stated as a premise.




The death penalty is appropriate for traitors because it is right to execute those who betray their own country and thereby risk the lives of millions.


This argument is circular because ““right”” means essentially the same thing as ““appropriate.”” In effect, the writer is saying that the death penalty is appropriate because it is appropriate.




Democracy is the best form of government yet created. Therefore, we must be vigilant in its defense; that is, we must be prepared to defend the right to freedom. Because this right is fundamental to any progressive form of government, it is clear that democracy is better than any other form of government.


This argument is circular. It is incumbent on the writer to give evidence or support for the conclusion. In this argument, though, the writer first states that democracy is the best government, the rest is merely ““noise,”” until he restates the conclusion.

Shifting the Burden of Proof


It is incumbent on the writer to provide evidence or support for her position. To imply that a position is true merely because no one has disproved it is to shift the burden of proof to others.




Since no one has been able to prove God’’s existence, there must not be a God.


There are two major weaknesses in this argument. First, the fact that God’’s existence has yet to be proven does not preclude any future proof of existence. Second, if there is a God, one would expect that his existence is independent of any proof by man.




Astronomers have created a mathematical model for determining whether life exists outside our solar system. It is based on the assumption that life as we know it can exist only on a planet such as our own, and that our sun, which has nine planets circling it, is the kind of star commonly found throughout the universe. Hence it is projected that there are billions of planets with conditions similar to our own. So astronomers have concluded that it is highly probable, if not virtually certain, that life exists outside our solar system. Yet there has never been discovered so much as one planet beyond our solar system.Hence life exists only on planet Earth.


This argument implies that since no planet has been discovered outside our solar system, none exist and therefore no life exists elsewhere in the universe. Hence the burden of proof is shifted from the arguer to the astronomers.


Reasoning by shifting the burden of proof is not always fallacious. In fact, our legal system is predicated on this method of thought. The defendant is assumed innocent until proven guilty. This assumption shifts the onus of proof to the state. Science can also validly use this method of thought to better understand the world—so long as it is not used to claim ““truth.”” Consider the following argument: ““The multitude of theories about our world have failed to codify and predict its behavior as well as Einstein’’s theory of relativity. Therefore, our world is probably ‘‘Einsteinian.’’”” This argument is strong so long as it is qualified with probably—otherwise it is fallacious: someone may yet create a better theory of our world.

Unwarranted Assumptions

The fallacy of unwarranted assumption is committed when the conclusion of an argument is based on a premise (implicit or explicit) that is false or unwarranted. An assumption is unwarranted when it is false— these premises are usually suppressed or vaguely written. An assumption is also unwarranted when it is true but does not apply in the given context—these premises are usually explicit. The varieties of unwarranted assumptions are too numerous to classify, but a few examples should give you the basic idea.


Example (False Dichotomy):


Either restrictions must be placed on freedom of speech or certain subversive elements in society will use it to destroy this country. Since to allow the latter to occur is unconscionable, we must restrict freedom of speech.


The writer offers two options: either restrict freedom of speech, or lose the country. He hopes the reader will assume that these are the only options available. This is unwarranted. He does not state how the socalled ““subversive elements”” would destroy the country, nor for that matter, why they would want to destroy it. There may be a third option that the author did not mention; namely, that society may be able to tolerate the ““subversives”” and it may even be improved by the diversity of opinion they offer.




To score in the ninetieth percentile on the GRE, one must study hard. If one studies four hours a day for one month, she will score in the ninetieth percentile. Hence, if a person scored in the top ten percent on the GRE, then she must have studied at least four hours a day for one month.


You may have noticed that this argument uses the converse of the fallacy ““Confusing Necessary Conditions with Sufficient Conditions”” mentioned earlier. In other words, it assumes that something which is sufficient is also necessary. In the given argument, this is fallacious because some people may still score in the ninetieth percentile, though they studied less than four hours a day for one month.




Of course Steve supports government sponsorship of the arts. He’’s an artist.


This argument is fallacious—and unfair—because it assumes that all artists support government sponsorship of the arts. Some artists, however, may have reasons for not supporting government sponsorship of the arts. For example, they may believe that government involvement stifles artistic expression. Or they may reject government involvement on purely philosophical grounds. The argument suggests a person’’s profession taints his opinion.

Appeal to Authority

To appeal to authority is to cite an expert’’s opinion as support for one’’s own opinion. This method of thought is not necessarily fallacious. Clearly, the reasonableness of the argument depends on the ““expertise”” of the person being cited and whether she is an expert in a field relevant to the argument. Appealing to a doctor’’s authority on a medical issue, for example, would be reasonable; but if the issue is about dermatology and the doctor is an orthopedist, then the argument would be questionable.


The legalization of drugs is advocated by no less respectable people than William F.Buckley and federal judge Edmund J. Reinholt. These people would not propose a social policy that is likely to be harmful. So there is little risk in experimenting with a one-year legalization of drugs.


The only evidence that the author gives to support her position is that respected people agree with her. She is appealing to the authority of others.

Personal Attack

In a personal attack (ad hominem), a person’’s character is challenged instead of her opinions, thereby deflecting attention away from a solid argument.


Politician: How can we trust my opponent to be true to the voters? He isn’’t true to his wife!


This argument is weak because it attacks the opponent’’s character, not his positions. Some people may consider fidelity a prerequisite for public office. History, however, shows no correlation between fidelity and great political leadership.


A reporter responded with the following to the charge that he resorted to tabloid journalism when he rummaged through and reported on the contents of garbage taken from the home of Henry Kissinger.

““Of all the printed commentary . . . only a few editorial writers thought to express the obvious point that when it comes to invasion of privacy, the man who as National Security Advisor helped to bug the home phones of his own staff members is one of our nation’’s leading practitioners.””
—Washington Monthly, October 1975


The reporter justifies his actions by claiming that Kissinger is guilty of wrongdoing. So, instead of addressing the question, he attacks the character of Henry Kissinger.

True But Irrelevant

This tactic is quite simple: the arguer bases a conclusion on information that is true but not germane to the issue.




This pain relief product is available over the counter or in a stronger form with a prescription. But according to this pamphlet, for the prescription strength product to be effective it must be taken at the immediate onset of pain, it must be taken every four hours thereafter, and it cannot be taken with any dairy products. So it actually doesn’’t matter whether you use the prescription strength or the over-the-counter strength product.


It is unreasonable to reject the effectiveness of a product merely because it has modest requirements for use. All medications have directions and restrictions. So, it cannot be concluded that just because the prescription strength product has certain guidelines and restrictions on its use that it is not more effective.


Identifying the conclusion of the argument you are given is essential in your analysis. From there, recognizing the author’’s premises will enable you to identify any flaws in the argument. Only then will you be able to write an effective analysis.

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