Online research in philosophy

What is the epistemological value of perceptual experience? In his recently influential paper, “The Skeptic and the Dogmatist”1, James Pryor develops a seemingly plausible answer to this question. Pryor’s answer comprises the following three theses: (F) “Our perceptual justification for beliefs about our surroundings is always defeasible – there are always possible improvements in our epistemic state which would no longer support those beliefs.” (517) (PK) “This justification that you get merely by having an experience as of p can sometimes suffice to give you knowledge that p is the case.” (520) (D) “When it perceptually seems to you as if p is the case, you have a kind of justification for believing p that does not presuppose or rest on your justification for anything else, which could be cited in argument (even an ampliative argument) for p. To have this justification for believing p, you need only have an experience that represents p as being the case. No further awareness or reflection or background beliefs are required.” (519) Let’s use the phrase “fallibilist dogmatism” to refer to the conjunction of (F), (PK), and (D).2 Pryor does not argue for either (F) or (PK) in his paper; he simply shares the widespread and plausible assumption that (F) and (PK) are both true. But the conjunction of (F) and (PK) implies that we can have knowledge on the basis of defeasible justification. And this view leads to paradox. Consider the following individually plausible but jointly incompatible statements.

The general conditions of epistemic defeat are naturally represented through the interplay of two distinct kinds of entailment, deductive and defeasible. Many of the current approaches to modeling defeasible reasoning seek to define defeasible entailment via model-theoretic notions like truth and satisfiability, which, I argue, fails to capture this fundamental distinction between truthpreserving and justification-preserving entailments. I present an alternative account of defeasible entailment and show how logic programming offers a paradigm in which the distinction can be captured, allowing for the modeling of a larger range of types of defeat. This is possible through a natural extension of the declarative and procedural semantics of Horn clauses.

The view that psychological episodes have a physical nature (physicalism) and the view that they have a mental nature (Cartesian dualism) can be distinguished from the view that they have a purely normative nature. I explore some strands of a distinct, fourth view: psychological episodes are what they are because of the actual and possible relations of defeasible justification in which they stand; defeasible justification is an internal relation; it is not at bottom a normative matter; rule-following presupposes such internal relations; to follow a rule is not to break it.

Joshua Thurow offers a defence of the claim that if a belief is defeasible by non-experiential evidence then it is defeasible by experiential evidence. He responds to an objection which I make against this claim, and offers two arguments in support of his own position. I show that Thurow's response misconstrues my objection, and that his supporting arguments fall short of their goal.

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 terms of the degrees of justification of all relevant premises and the strengths of all relevant reasons.

In a recent and interesting paper “Experientially Defeasible A Priori Justification,” Joshua Thurow argues that many a priori justified beliefs are defeasible by experience. The argument takes the form of an objection against Albert Casullo’s recent book, A Priori Justification, where Casullo, according to Thurow, denies that if a justified belief is non-experientially defeasible, then that belief is also experientially defeasible. This paper critically examines Thurow’s two arguments in the first two sections I–II. In the last section, III, an alternative line of argument for Thurow’s thesis is suggested that employs other parts of the framework that Casullo provides—especially the thesis of overdetermination of justification. It will be argued that the prospects for this suggestion are brighter than for bothof Thurow’s arguments.

It is widely assumed that justification is defeasible, e.g. that under certain conditions counterevidence removes prior justification of beliefs. In this paper I will first (sect. 1) explain why this feature of justification poses a prima facie problem for reliabilism. I then will try out different reliabilist strategies to deal with the problem. Among them I will discuss conservative strategies (sect. 2), eliminativist stragies (sect. 3) and revisionist strategies (sect. 4). In the final section I will present an improved revisionist approach to defeaters that is able to overcome the main shortcomings of the other approaches.

Heuristics can be regarded as justifying the actions and beliefs of problem-solving agents. I use an analysis of heuristics to argue that a symbiotic relationship exists between traditional epistemology and contemporary artificial intelligence. On one hand, the study of models of problem-solving agents usingquantitative heuristics, for example computer programs, can reveal insight into the understanding of human patterns of epistemic justification by evaluating these models'' performance against human problem-solving. On the other hand,qualitative heuristics embody the justifying ability of defeasible rules, the understanding of which is provided by traditional epistemology.

In his recent book Albert Casullo rejects the claim that if a belief is defeasible by non-experiential evidence then it is defeasible by experiential evidence. This claim is a crucial premise in a simple argument for the experiential defeasibility of a priori justification. I defend the premise against Casullo's objection, the main problem with which is that he does not take into account the evidential role of multiple corroborating sources of testimony. I conclude that the crucial premise is true and that the simple argument is sound; thus many of our a priori justified beliefs are experientially defeasible.

both the initial justification for adopting it and the justification for retaining it provided by seeming memories. This view captures our intuitions about justification in several cases, while none of the alternative views can.