Abstract
How should we evaluate an argument in which two witnesses independently testify to some claim? In fact what would happen is that the testimony of the second witness would be taken to corroborate that of the first to some extent, thereby boosting up the plausibility of the first argument from testimony. But does that commit the fallacy of double counting, because the second testimony is already taken as independent evidence supporting the claim? Perhaps the corroboration effect should be considered illogical, since each premise should be seen as representing a separate reason in a convergent argument for accepting the claim as plausible. In this paper, we tackle the problem using argumentation schemes and argument diagramming. We examine a number of examples, and come up with two hypotheses that offer methods of analyzing and evaluating this kind of evidence.
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Notes
Many of the issues discussed relate to questions studied in a recent paper on argument evaluation (Goddu 2003), but we have no space to comment on them specifically, in order to fit the length requirements.
Helpful discussions of how these tools are proving to be important both in artificial intelligence and law are provided in (Reed and Norman 2003).
The original version of the clock and gun case can be found in (Walton 1984, p. 16).
At any rate, it would make it stronger, and let’s say that in the kind of case we are considering, depending on how we are rating argument strength by some standard, it would make it very strong.
References
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Walton, D., Reed, C. Evaluating Corroborative Evidence. Argumentation 22, 531–553 (2008). https://doi.org/10.1007/s10503-008-9104-0
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DOI: https://doi.org/10.1007/s10503-008-9104-0