The Fallacy of ?Ad Ignorantiam?
John A. Woods, Douglas Walton · dialectica · 1978
This paper outlines a three-part analysis of the traditional informal fallacy of ad ignorantiam. As initially characterized, the fallacy consists in arguing that failure to prove falsity (truth) implies the truth (falsity) of a proposition. First, the fallacy is located within confirmation theory as a confusion between the categories of “lack of confirming evidence” and “presence of disconfirming evidence”. Second, the structure of the fallacy can be seen as an illicit negation shift in Hintikka-style epistemic logic. Third, the fallacy can be studied as an attempt to unfairly shift the burden of proof in a dialectical game. We suggest that research on ad ignorantiam needs a broadening of the scope of philosophical logic to encompass concepts of correct argument in these three contexts.