Media Argumentation by Douglas Walton | Excerpt

The following excerpt about evaluating appeals to expert opinion (aka appeal to authority) is from Professor Douglas Walton's Media Argumentation: Dialectic, Persuasion, and Rhetoric.

[I]n court, a ballistics expert may be called in as a witness to testify about a bullet found at a crime scene. The first component of the argumentation scheme for argument from expert opinion is the following form of argument.

Form of Argument from Expert Opinion

Major Premise: Source E is an expert in subject domain S containing proposition A.
Minor Premise: E asserts that proposition A (in domain S) is true (false).
Conclusion: A may plausibly be taken to be true (false).

Argument from expert opinion is typically a presumptive form of argument, meaning that it carries tentative probative weight in a dialogue. But presumptive arguments of this kind are defeasible, meaning that they are subject to defeat at some next point in the dialogue. As the logic textbooks tell us, appeal to expert opinion can even be fallacious in some cases. The problem is that there is a natural tendency to defer to an expert, and it is easy to give in to this tendency uncritically, without making the effort to ask critical questions. Thus the second component of the argumentation scheme for appeal to expert opinion is the following list of six basic critical questions.


Critical Questions for the Argument from Expert Opinion

1. Expertise Question: How credible is E as an expert source?
2. Field Question: Is E an expert in the field that A is in?
3. Opinion Question: What did E assert that implies A?
4. Trustworthiness Question: Is E personally reliable as a source?
5. Consistency Question: Is A consistent with what other experts assert?
6. Backup Evidence Question: Is A’s assertion based on evidence?

The evaluation of argumentation based on appeal to expert opinion takes the form of a dialogue. If a proponent puts forward an argument that has the form of the argumentation scheme above, and the premises are based on good evidence, then the argument carries probative weight.

This means that the respondent in the dialogue is obliged to provisionally accept the conclusion of the argument. But the respondent also has the option of asking appropriate critical questions. If he asks such a critical question, the proponent has the burden of proof, meaning that he must either answer the question or the argument is defeated. That is, the proponent must answer the critical question adequately or he must give up the appeal to expert opinion as an argument carrying presumptive weight in the dialogue.


Media Argumentation: Dialectic, Persuasion, and Rhetoric by Douglas Walton
Copyright © 2007 Douglas Walton.  Reprinted with the permission of Cambridge University Press.