INFERENCE PATH

As a part-time adjunct professor, I am fascinated by argument schemes. Ever since I was introduced to them by the incredible work of Professor Douglas Walton, I have sought to better understand them. To me that understanding is an essential path to more fully appreciating practical reasoning from a pedagogical perspective.

But as a full-time litigator and appellate attorney, I searched for a way to make them more relevant in my practice. (My livelihood depends on whether I can actually persuade the judge using argument patterns.) Of course, the application to litigation of “critical questions” is obvious. An explicit list of the assumptions that accompany certain patterns of reasoning is very useful. For example, knowing the inherent assumptions that accompany testimony (e.g., lack of bias, observational ability) makes the targets of cross-examination readily apparent. But the direct application of the patterns themselves had been less obvious to me.

My concern had been that typically argument schemes are presented in their enthymematic (i.e. missing premise) structure. Asking judges to fill in the blanks is a risky business (e.g., judges or juries have never learned the abstract patterns to begin with and inferential leaps by their very nature are risky.)

For example, consider the following argument scheme “Appeal to Expert Opinion”  (Walton, p. 3):

• E is an expert in domain S.
• E asserts that C is known to be true.
• C is within S.
• Therefore, C may be plausibly taken to be true.

There are two difficulties with this enthymematic form of an argument scheme for use in an argument map for a judge or juror. First, there is an obvious missing premise. The inference bridge cannot, no matter how the pieces are linked, reach the conclusion. The judge or juror must make a leap. The second difficulty is that the linkages of the premises are not (except for a student of logic) obvious.

One option, suggested by Walton and Reed, is to use an apparent modus ponens form that reflects “a more  explicit account of the structure of the inference that makes the warrant that the argument is based on more visible.”

• E is an expert in domain S.
• E asserts that C is known to be true.
• C is within S.
• If E is an expert in subject domain S and asserts that C is known to be true, then C may plausibly be taken to be true.
• Therefore, C may be plausibly taken to be true.

The use of this more explicit form solves the first obstacle since the missing premise is made apparent. As Walton and Reed point out, however, Version 2 leads to a controversy: How can a defeasible argument structure use a deductively valid argument form (e.g., modus ponens)? They provide an elegant solution. They suggest that there is a strict modus ponens and a defeasible modus ponens. The distinction depends on whether the conditional is strict or defeasible.

But the second obstacle (i.e., abstract linkage) still exists. While a modus ponens form is obvious to the readers of this blog, it is not obvious to judges and typical jurors who do not read it. Research has shown, however, that transitivity is easily perceived. So a more complete solution might be to use essential Predication TRANSITIVITY to structure any argument scheme.

And the possible controvery of using an argument form of logical necesssity for a defeasible argument can be avoided as suggested for modus ponens by Walton and Reed. Generalizations used in the essential Predication TRANSITIVITY path can be either strict or defeasible. The use of qualifiers can make this apparent.  So the result is, I suggest, that there are two kinds of inference paths of essential Predication TRANSITIVITY, namely, strict and defeasible. (This form may also be helpful in developing justifications of argument schemes.)

For purposes of litigation, the argument map also needs to make a visual distinction between inferentially linked premises and assumptions while still maintaining both of them within the inferential network of the argument scheme. The practice of adding assumptions as attached notes of “critical questions” or intermingled with linked premises just creates, in my experience, confusion and obscures the details of the interconnecting web of the argument. see http://wiki.austhink.com/Brief+explanation+of+Argumentation+Schemes.