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An understanding of logical fallacy is important to the academic writer for two reasons.  First, during the research phase of the writing project, the writer will read and critically evaluate a variety of resource documents. Each item must be asssessed in both evidence and reasoning. The main determinant of acceptable reasoning is the absence of logical fallacy. (The other is the strength and validity of the proffered evidence.) Second, as the writer begins the process of crafting his or her words into a meaningful fabric, it is vital to avoid making these sorts of reasoning errors.  The point of any argument is to provide substantial reasons in support of some conclusion; however, an argument commits a fallacy when the reasons offered do not, in fact, support the conclusion. Presented here are fifty-four types of logical fallacy--each explained clearly along with strategies to identify and attack them.  If the writer understands how faulty reasoning can be attacked, prevention of such errors is considerably easier.

Fallacies of Definition

Frequently writers use a definition to  make words or concepts clear and unambiguous. Definitions explain precisely what a word or term means. The mark of a good definition lies in its capability to enable a reader to identify instances of the word or concept without additional help. Readera should be able to correctly identify every instance of the defined concept without incorrectly including other things or struggling to tell the difference between them. The following fallacies demonstrate definitional problems.

• Overly Broad Definition
• Overly Narrow Definition
• Failure to Elucidate
• Circular Definition
• Conflicting Conditions

Fallacies of Distraction

Logical operators can be improperly used in an argument to distract the reader from a false conclusion. Each of the following fallacies demonstrates this technique:

• The False Dilemma
• Arguing from Ignorance (argumentum ad ignorantiam)
• The Slippery Slope 
• The Complex Question (plurium interrogationum)

Fallacies of Materiality

Weak and uncompelling arguments are sometimes masked by shifting the readers attention away from the substance of the matter by raising an immaterial (doesn't have anything to do with the case) argument such as an appeal to the reader's emotions or other psychological factors or by attacking the author. There are a great many fallacies of this type. 

• Appeal to Authority (argumentum ad verecundiam)
• Appeal to Convenience (argumentum ad convenientiam)
• Appeal to Consequences (argumentum ad consequentiam)
• Appeal to Envy (argumentum ad invidiam)
• Appeal to Force (argumentum ad baculum)
• Appeal to Nature (argumentum ad naturum)
• Appeal to the Moon (argumentum ad lunam)
• Appeal to Novelty (argumentum ad novitatem)
• Appeal to Numbers (argumentum ad numerum)
• Appeal to Pity (argumentum ad misercordiam)
• Appeal to Popularity (argumentum ad populum)
• Appeal to Poverty (argumentum ad lazarum)
• Appeal to Tradition (argumentum ad antiquitatem)
• Appeal to Wealth (argumentum ad crumenam)
• Attacking the Person (argumentum ad hominem)
• Use of Prejudicial Language
• Anonymous Authority
• Style over Substance

Fallacies of Ambiguity

When writers use ambiguous or vague language, readers can become easily confused and lose the intended meaning.  When a word or phrase has more than one meaning, it is said to be ambiguous; however, if it lacks distinct meaning it is said to be vague.  The following fallacies illustrate these problems.

• Equivocation
• Amphibole
• Accent

Fallacies of Induction

When a writer makes assumptions about the whole of something based on the characteristics of just a part of it, we refer to that as inductive reasoning or induction. So, for example, if you open a bag of colored candy and pour a small amount in your hand and notice that one third of them are red, and from that, you reason that one third of the candy in the bag is red, your reasoning was inductive.

Inductive reasoning, then, consists on inferring from the properties of a sample to the properties of a population as a whole and depends on the presence of a similarity between the sample and the population. In fact, the science of statistics has several tests to measure this very similarity. The more similar the sample is to the population as a whole, the more reliable will be the inductive inference. On the other hand, if the sample is relevantly dissimilar to the population, then the inductive inference will be quite unreliable.  No inductive inference is totally perfect, thus, it can sometimes fail even though it seems reasonable on its face. Even though the premises are true, the conclusion could be false.Nonetheless, a good inductive inference gives us a reason to believe that the conclusion is probably true--and that's the value of it.

• Hasty Generalizations
• Unrepresentative Sample
• False Analogies
• Slothful Induction
• Fallacy of Exclusion

Fallacies of Explanation

Writers often seek to offer explanations to some event or phenomenon, or in other words, answer the question "why?" A proper explanation is based on a soundly constructed  theory. A theory, in this sense, is a  tentative explanation for a phenomenon that can be tested by further investigation using statistical analysis, scientific method, observation, or controlled test. The following fallacies outline various ways theories can be defective.

• Subverted Support
• Non-support
• Untestability
• Limited Scope
• Limited Depth

Fallacies of Cause

Most people readily accept a conclusion that one thing causes another, yet the relationship between cause and effect is seldom that simple. Moreover, such assumptions tend to be prone to error. If  possible exceptions are factored out, the rule of cause and effect, simply stated,  is that  a causal relationship may be assumed to exist if the presence of the cause results in the effect AND if the absence of the cause results in the absence of the effect. The following five fallacies are exemplify these errors:

• Coincidental Correlation (post hoc ergo propter hoc)
• Single Causation -- Joint Effect
• Genuine but Insignificant Causation
• Relational Error
• Complex Causation

Missing the Point

Occasionally a writer may do a spectacular job writing a great answer--but for the wrong question. The following three fallacies share a general failure to prove that the conclusion reached is true.

• Begging the Question (petitio principii)
• Irrelevant Conclusions  (ignoratio elenchi)
• Straw Man

Categorical Errors

If the writer mistakenly assumes that the whole is nothing more than the sum of its parts, he or she may have committed a category error. This is because things joined together do not always have the same properties as a whole than any of them do separately. So, for example, when one combines flour, sugar, and eggs together and bakes the result in the oven, the resulting cake is nothing like any of the ingredients from which it was made.

• Composition
• Division

Non-Sequitur

Sometimes a writer presents an argument where his or her conclusion simply does not follow from the offered premises and these errors are called non-sequiturs. Non-sequitur errors are the errors associatiated with defective conditional syllogisms.  Conditional, or if-then, syllogisms refer to reasoning in the form of "if" something is true, "then" something else must be true as well.  The following three fallacies demonstrate how this can happen.

• Affirming the Consequent
• Denying the Antecedent
• Inconsistent Argument

Syllogistic Errors

Syllogistic errors are the errors associated with categorical syllogism--a form of reasoning that describes the relationships between groups of things in the general form of either "All A are B", "Some A are B",  "Some A are not B," or "No A are B" which are known as premises.  All syllogisms have exactly three terms known as the major premise, the minor premise, and the conclusion. The idea is that, taken together, the major and minor premises should result in the conclusion.  The following premises illustrate the possible errors that might cause defective syllogisms.

• Fallacy of Four Terms
• Undistributed Middle
• Illicit Major
• Illicit Minor
• Exclusive Premises
• Drawing an Affirmative Conclusion from a Negative Premises
• Existential Fallacy

Statistical Generalization

Sometimes a writer will make a statement which is usually, but not always, true. Very often these are expressed using the word "most", as in "Most conservatives favor welfare cuts." Sometimes the word "generally" s used, as in "Liberals generally support welfare programs." Or, sometimes, no specific word is used at all, as in: "Conservatives favor welfare cuts while liberals support welfare increases." These fallacies of statistical generalization occur because the generalization is not always true. Thus, an author commits a fallacy when he or she treats a statistical generalization as though it were always true. There are two forms of this fallacy:

• Accident
• Converse Accident

Conclusion

This list of fallacies is by no means exhaustive but does include the ones most likely to be encountered. As you review source material for your paper, watch carefully for these forms of errors along with possible evidentiary errors. Your paper can be no better than the source materials you select and, if those are riddled with faulty reasoning or evidence, your conclusion will also be faulty.

By Douglas E. Greathouse, MA