Floating conclusions and zombie paths: Two deep difficulties in the “directly skeptical” approach to defeasible inheritance nets

Skepticism and floating conclusions

“…This phrase, coined by Makinson and Schlechta [9], nicely captures the picture of these conclusions as floating above the different and conflicting arguments that might be taken to support them.…”

Adaptive Logic Characterizations of Input/Output Logic

“…(Full meet constrained output) (H, A). 17 For readers unfamiliar with the notions of skeptical and credulous consequence, we refer to [22,28] for more details.…”

“…As explained before, such cases are trivialized by our logics whereas (in case (ID) / ∈R) neither out ∩ R (G, A, C) nor out ∪ R (G, A, C) need be trivial. 28 Proof outline. In the remainder of this section, we broadly explain how we prove the equivalence set out in Theorem 3 between the adaptive consequence relations on the one hand, and the constrained I/O operations on the other.…”

“…Using terminology from default logic, conclusions such as c ∨ d may be called floating conclusions [28]. In our terms, they can be defined as those formulas in out ∩ R (G, A, C) which cannot be generated from the I/O pairs that are shared by every member of maxfamily R (G, A, C).…”

Which style of reasoning to choose in the face of conflicting information?

“…From both we can derive that he arrives either at 10am or at 1pm. There is a vivid debate concerning the question whether and when floating conclusions should be accepted (see [7,10,12]). In [19] the notion of floating conclusions has been linked to the strategies of adaptive logics: according to the minimal abnormality strategy they are accepted, while according to the reliability strategy they are rejected.…”