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Writing an Argument: Flaws in Logic

The following flaws in logic can make your readers mistrust you as a writer. Watch out for these flaws as you check your drafts.
1. Sweeping generalizations  Generalizations can sometimes be so broad that they fall into stereotyping: "All British people are stiff and formal" or "The only thing that concerns students is grades."
2. Hasty conclusions with inadequate support  To convince your readers of the validity of a generalization, you need more than one personal example. "My friend Arecelis had a terrible time in a bilingual school. This experience shows that bilingual education has failed."
3. Non sequitur  Non sequitur is Latin for "It does not follow." This sentence is a non sequitur: "Anna Quindlen writes so well that she would make a good teacher." The connection between writing and teaching has not been established.
4. Causal fallacy  You are guilty of causal fallacy if you assume that one event causes another when the second merely follows the first in time. (The Latin name for this logical flaw is post hoc, ergo propter hoc: "after this, therefore because of this.") Example: "The economy collapsed because a new president was elected."
5. Ad hominem attack  Ad hominem (Latin for "to a person") refers to an argument that appeals to personal considerations rather than to logic or reason. Avoid using arguments that seek to discredit an opinion through personal criticism, such as "The new curriculum should not be adopted. The administrator who favors it doesn't even live near this college."
6. Circular reasoning  In an argument that uses circular reasoning, the evidence and the conclusion restate each other, thus proving nothing: "That rich man is smart because wealthy people are intelligent."
7. False dichotomy or false dilemma  Either/or arguments reduce complex problems to two simplistic alternatives without exploring them in depth or considering other alternatives. For example, an essay that builds its argument on the assertion "To improve education, the Board can either hire more teachers or build more schools" presents a false dichotomy. Those two options are not the only ways to improve education.
See also
Basic Strategies
Issue and Audience
Claim, Reasons, and Evidence
Methods of Reasoning