Perception and Persuasion in Legal Argumentation: Using Informal Fallacies and Cognitive Biases to Win the War of Words

44 Pages Posted: 21 Mar 2013 Last revised: 28 Mar 2013

See all articles by Cory Clements

Cory Clements

affiliation not provided to SSRN

Date Written: March 1, 2013


When zealously advocating a client’s position, the lawyer’s ultimate goal is winning. To win, however, the lawyer must convince a judge or jury to accept the lawyer’s (and reject opposing counsel’s) position. The best type of advocate accomplishes this goal using various rhetorical techniques, attempting to manage other people’s perceptions of such things as the facts, the lawyer’s own theory of the case, the credibility of eyewitness testimony, the weaknesses of opposing counsel’s claims, and the praiseworthiness of the lawyer’s own client. By design, we have an adversary system.

But how does the lawyer successfully convince the fact finder that the lawyer’s (and not opposing counsel’s) position is aligned with justice? Success inevitably boils down to persuasive legal argumentation. If the lawyer’s ultimate goal is winning, the lawyer must master the art of persuasion. For the art of persuasion is intimately connected with the psychological process of perception. And perception is what convinces people whether to accept or reject the lawyer’s argument.

In this Comment, I propose an account of legal argumentation that explains the relationship between mental processes that psychologists label cognitive biases and legal arguments that philosophers label informal fallacies. Cognitive biases are errors in our thinking and reasoning, which alter our perceptions. Informal fallacies are verbal or written arguments containing material flaws, which enhance their persuasiveness. I also describe the process of persuasion at play when the lawyer uses legal arguments that contain informal (material) fallacies. By using legal arguments that contain informal fallacies, the lawyer can play upon the listener’s inherent cognitive biases to persuade the listener to see things the same way the lawyer does. When lawyers use these rhetorical techniques — whether before or during trial proceedings — they induce in most listeners erroneous perceptions that can, and often do, powerfully alter their listeners’ beliefs.

My first general purpose is to explain what lawyers and judges can learn from psychologists’ and philosophers’ insights on legal argumentation. There is a connection between perception and persuasion — namely, that cognitive biases (linked to perception) and informal fallacies (linked to persuasion) are merely two different labels used to describe faulty reasoning as it occurs in one of three phases in the reasoning process: (1) the arguer’s mental process in which a specific bias influences how she interprets her perceptions and how she is persuaded to believe something; (2) the arguer’s rhetorical process in which she uses a specific tool or argument to persuade the listener to perceive and believe as she believes; and (3) the listener’s mental process in which a specific bias influences his perceptions of the arguer’s reasoning and persuades him to believe as she does.

My second general purpose is to promote a new framework for viewing the use of informal fallacies in legal argumentation. Lawyers use informal fallacies as a strategy of persuasion to induce cognitive biases in other people’s thinking, to effectively manage their perceptions, and to ultimately change their beliefs. While informal fallacies can be used deceptively — and philosophers condemn and try to excise them from argumentation completely — they can play an essential role in good legal argumentation and effective advocacy. Informal fallacies may help to persuade the listener to actually care about the outcome of a case and to see things the way the lawyer sees them. Similarly, while cognitive biases are generally viewed as a hindrance to the truth — and psychologists catalogue and study their negative impact on eyewitness testimony — they can play an essential role in good legal proceedings. Cognitive biases may help even the most simple-minded listener to perceive each lawyer’s version of the case and to determine which to believe. Thus, good legal arguments and proper judicial proceedings can still involve both types of error in reasoning.

Keywords: legal argumentation, perception, cognitive bias, persuasion, informal logical fallacies

Suggested Citation

Clements, Cory, Perception and Persuasion in Legal Argumentation: Using Informal Fallacies and Cognitive Biases to Win the War of Words (March 1, 2013). 2013 Brigham Young University Law Review 319, Available at SSRN:

Cory Clements (Contact Author)

affiliation not provided to SSRN

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