This paper exhibits some problematic cases of defeasible or nonmonotonic reasoning that tend to be handled incorrectly by all of the theories of defeasible and nonmonotonic reasoning in the current literature. The paper focuses particularly on default logic, circumscription, and the author’s own argument-based approach to defeasible reasoning. A proposal is made for how to deal with these probl...

Justification Logic is a family of epistemic logical systems obtained from modal logics of knowledge by adding a new type of formula t:F , which is read t is a justification for F . The principal epistemic modal logic S4 includes Tarski’s well-known topological interpretation, according to which the modality 2X is read the Interior of X in a topological space (the topological equivalent of the ...

Justification logics are refinements of modal logics, where justification terms replace modalities. Modal and justification logics are connected via the so-called realization theorems. We develop a general constructive method of proving the realization of a modal logic in an appropriate justification logic by means of cut-free modal nested sequent systems. We prove a constructive realization th...

According to a standard view of the second law of thermodynamics, our belief in the second law can be justified by pointing out that low entropy macrostates are less probable than high entropy macrostates, and then noting that a system in an improbable state will tend to evolve toward a more probable state. I would like to argue that this justification of the second law of thermodynamics is fun...

Committees of classifiers with learning capabilities have good performance in a variety of domains. We focus on committees of agents with learning capabilities where no agent is omniscient but has a local, limited, individual view of data. In this framework, a major issue is how to integrate the individual results in an overall result—usually a voting mechanism is used. We propose a setting whe...

n June 1997 a sixteen-year-old girl named Shannon Nixon began to I feel ill. Her parents belonged to the Faith Tabernacle Church, one of a number of American sects which believe that illness should be treated spiritually rather than medically. Accordingly, the Nkons prayed for Shannon and took her to be anointed at their church. Shannon reported that she felt better and that the spiritual treat...

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The question addressed in this paper is how the degree of justification of a belief is determined. A conclusion may be supported by several different arguments, the arguments typically being defeasible, and there may also be arguments of varying strengths for defeaters for some of the supporting arguments. What is sought is a way of computing the “on sum” degree of justification of a conclusion...

In an earlier paper we have shown that a proposition can have a welldefined probability value, even if its justification consists of an infinite linear chain. In the present paper we demonstrate that the same holds if the justification takes the form of a closed loop. Moreover, in the limit that the size of the loop tends to infinity, the probability value of the justified proposition is always...

Justification logics are logics of knowledge in which explicit reasons are formally represented. Standard logics of knowledge have justification logic analogs. Connecting justification logics and logics of knowledge are Realization Theorems. In this paper we give a new, constructive proof of the Realization Theorem connecting S5 and its justification analog, JS5. This proof is, I believe, the s...