Defeasibility Theory of Knowledge

Many epistemologists are enamored with a defeat condition on knowledge. In this paper we present some implementation problems for defeatism, understood along either internalist or externalist lines. We then propose that one who accepts a knowledge norm of belief, according to which one ought to believe only what one knows, can explain away much of the motivation for defeatism. This is an important result, because on the one hand it respects the plausibility of the intuitions about defeat shared by many (...) in epistemology; but on the other hand, it obviates the need to provide a unified account of defeat which plays well with the most plausible views of how knowledge fits with evidential probability. (shrink)

Defeasibility, most generally speaking, means that given some set of conditions A, something else B will hold, unless or until defeating conditions C apply. While the term was introduced into philosophy by legal philosopher H.L.A. Hart in 1949, today, the concept of defeasibility is employed in many different areas of philosophy. This volume for the first time brings together contributions on defeasibility from epistemology , legal philosophy and ethics and the philosophy of action . The volume ends with an extensive (...) bibliography. (shrink)

This is a reply to John N. Williams’ paper “Not Knowing You Know: A New Objection to the Defeasibility Theory of Knowledge'” (2015). That paper argues that Peter Klein’s defeasibility theory of knowledge excludes the possibility of one knowing that one has (first-order) a posteriori knowledge. Klein himself answered a version of this objection in his (1971). Williams’ paper adds a new twist to the 1971 objection. I argue that Williams’ objection misses its target because of this new twist.

This is a collection of new essays written in honor of the work of Peter D. Klein, who has had and continues to have a tremendous influence in the development of epistemology. The essays reflect the breadth and depth of Klein’s work by engaging directly with his views and with the views of his interlocutors.

Applying a theory of psychological modularity, I argue for a theory of defeasibility conditions for the epistemic justification of perceptual beliefs. My theory avoids the extremes of holism (e.g., coherentism and confirmation holism) and of foundationalist theories of non-inferential justification.

The paper considers contemporary models of presumption in terms of their ability to contribute to a working theory of presumption for argumentation. Beginning with the Whatelian model, we consider its contemporary developments and alternatives, as proposed by Sidgwick, Kauffeld, Cronkhite, Rescher, Walton, Freeman, Ullmann-Margalit, and Hansen. Based on these accounts, we present a picture of presumptions characterized by their nature, function, foundation and force. On our account, presumption is a modal status that is attached to a claim and has the (...) effect of shifting, in a dialogue, a burden of proof set at a local level. Presumptions can be analysed and evaluated inferentially as components of rule-based structures. Presumptions are defeasible, and the force of a presumption is a function of its normative foundation. This picture seeks to provide a framework to guide the development of specific theories of presumption. (shrink)

John Hawthorne’s marvelous book contains a wealth of arguments and insights based on an impressive knowledge and understanding of contemporary discussion. We can address only a small aspect of the topic. In particular, we will offer our own answers to two questions about knowledge that he discusses.

Richard Feldman and William Lycan have defended a view according to which a necessary condition for a doxastic agent to have knowledge is that the agent’s belief is not essentially based on any false assumptions. I call this the no-essential-false-assumption account, or NEFA. Peter Klein considers examples of what he calls “useful false beliefs” and alters his own account of knowledge in a way which can be seen as a refinement of NEFA. This paper shows that NEFA, even given Klein’s (...) refinement, is subject to counterexample: a doxastic agent may possess knowledge despite having an essential false assumption. Advocates of NEFA could simply reject the intuition that the example is a case of knowledge. However, if the example is interpreted as not being a case of knowledge, then it can be used as a potential counterexample against both safety and sensitivity views of knowledge. I also provide a further case which, I claim, is problematic for all of the accounts just mentioned. I then propose, briefly, an alternative account of knowledge which handles all these cases appropriately. (shrink)

Philosophers have sought to characterize a type of knowledge — what I call real knowledge — which is significantly different from the ordinary concept of knowledge. The concept of knowledge as true, justified belief — what I call knowledge simpliciter — failed to depict the sought after real knowledge because the necessary and jointly sufficient conditions of knowledge simpliciter can be felicitously but accidentally fulfilled. Real knowledge is knowledge simpliciter plus a set of requirements which guarantee that the truth, belief (...) and justification conditions are not accidentally conjoined. Two of those requirements have received considerable attention in recent literature by the defeasibility theorists and the causal theorists. I argue that a third requirement is needed to block the merely coincidental cosatisfaction of the belief and justification conditions and to capture our intuitions about the epistemic agent who possesses real knowledge. That condition ascribes a disposition to the real knower to believe all and only justified propositions in virtue of his/her belief that the propositions are justified. Two consequences of that requirement are discussed: (1) if S really knows that p, then S knows simpliciter that S knows simpliciter that p and (2) the iterative feature of real knowledge mentioned in (1) provides a basis for the rejection of a particularly pernicious form of scepticism. (shrink)

Rich with historical and cultural value, these works are published unaltered from the original University of Minnesota Press editions.

The recently offered, Purported counter-Examples to justified, True belief analyses of knowledge are looked at with some care and all found to be either incoherent or inconclusive. It is argued that justified, True belief analyses are based on sound insight into the concept of knowledge. The distinction between having been justified in claiming to know something and actually having known it is used in an effort to get the discussion of knowledge back on the right track.

In Epistemic Entitlement. The Right to Believe Hannes Ole Matthiessen develops a social externalist account of epistemic entitlement and perceptual knowledge. The basic idea is that positive epistemic status should be understood as a specific kind of epistemic right, that is a right to believe. Since rights have consequences for how others are required to treat the bearer of the right, they have to be publicly accessible. The author therefore suggests that epistemic entitlement can plausibly be conceptualized as a status (...) that is grounded in a publicly observable perceptual situation, rather than in a perceptual experience as current theories of epistemic entitlement state. It is then argued that such a social externalist account of entitlement, in which the perceiver's epistemic perspective becomes relevant only in the exceptional case where an entitlement is challenged, can nevertheless do justice to our central intuitions about first-personal epistemic phenomenology. (shrink)

In this paper I discuss the relation between various properties that have been regarded as important for determining whether or not a belief constitutes a piece of knowledge: its stability, strength and sensitivity to truth, as well as the strength of the epistemic position in which the subject is with respect to this belief. Attempts to explicate the relevant concepts more formally with the help of systems of spheres of possible worlds (à la Lewis and Grove) must take care to (...) keep apart the very different roles that systems of spheres can play. Nozicks sensitivity account turns out to be closer to the stability analysis of knowledge (versions of which I identify in Plato, Descartes, Klein and Lehrer) than one might have suspected. (shrink)

When epistemologists talk about knowledge, the discussions traditionally include only a small class of other epistemic notions: belief, justification, probability, truth. In this paper, we propose that epistemologists should include an additional epistemic notion into the mix, namely the notion of assuming or taking for granted.

I objected that the defeasibility theory of knowledge prohibits you from knowing that you know that p if your knowledge that p is a posteriori. Rodrigo Borges claims that Peter Klein has already satisfactorily answered a version of my objection. He attempts to defend Klein’s reply and argues that my objection fails because a principle on which it is based is false.I will show that my objection is not a version of the old one that Klein attempts (unsuccessfully) to address, (...) that Borges’ defence of Klein’s reply fails and that his argument against my new objection leaves it untouched. (shrink)