Looking to achieve your communication strategy primarily through logos, an appeal to reason? That means you'll be constructing an argument, supporting a position, making an assertion relying largely on facts, inferences, data. And though your strategy will likely entail using some measure of ethos and pathos, the strength of your argument must possess the greatest persuasive force.

An appeal to reason must demonstrate solid if not unassailable logic – its ideas connected and their relationship established, its steps ordered, each basis or cause rationally explained, each claim or assertion supported by verifiable proof.

Not so easy to do well, sometimes. But you can make your case stronger by searching for logical fallacies in each part of an argument you construct for a document or presentation. Dozens of such fallacies exist. Think of them as errors or mistakes in reasoning, breaks in logic that weaken and sometimes destroy an argument. They also affect ethos, the audience's assessment of a speaker's or writer's credibility; that assessment may be lowered when an audience perceives that flawed reasoning grows from intellectual inferiority, lack of character, or nefarious purpose.


Here's a list of ten common logical fallacies. Should you find any as you prepare your text, revise them by correcting your reasoning, recasting your point, locating more reputable evidence, and/or shoring up your explanations.

  1. Confirmation Bias (Cherry-Picking, Biased Interpretation): Seeks or notices only the information or evidence that validates already-held beliefs; dismisses or suppresses evidence that violates beliefs; interprets evidence or information to conform to beliefs
  2. False Dichotomy (Either/Or): Presents a complex issue or problem as having only two sides or solutions although other sides, positions, and solutions exist
  3. Hasty Generalization: Basing a position or assertion on insufficient or irrelevant evidence
  4. Hypocrisy (tu quoque or "you also"): Alleges that another's position is flawed because his or her behavior is inconsistent with the claims that position makes
  5. Personal Attack (ad hominum): Berates the opposition by calling names or insulting character instead of focusing on the opposition's argument or position
  6. Post hoc ergo propter hoc (after this, therefore, because of this): Asserts that one event caused another simply because one followed the other
  7. Popular Opinion (Communal Reinforcement): Assumes that something must be true, correct, or right because many people believe it to be
  8. Slippery Slope: Presents a first undesired action or condition as inevitably leading to a final and greater undesired action or condition as a way of arguing against the acceptance of the first one
  9. Sweeping Generalization: Making a claim that is insupportably broad and does not allow for exceptions
  10. Tradition: Maintains that a condition, definition, or action must be true or right because it has "always" been believed to be true or right

Logical fallacies divert attention, fail to engage issues, and provide untenable reasons and/or evidence, losing the legitimately persuasive force their authors were likely trying to exert. But sometimes authors deliberately employ logical fallacies for deceptive purposes. Stay aware, then, as a writer and a presenter but also as an audience member. Remain alert for any weak links in a chain of reasoning, for it is at that link that reason ends.