A perfectly matched layer (PML) absorbing material composed of a uniaxial anisotropic material is presented for the truncation of finite-difference time-domain (FDTD) lattices. It is shown that the uniaxial PML material formulation is mathematically equivalent to the perfectly matched layer method published by Berenger (see J. Computat. Phys., Oct. 1994). However, unlike Berenger's technique, the uniaxial PML absorbing medium presented in this paper is based on a Maxwellian formulation. Numerical examples demonstrate that the FDTD implementation of the uniaxial PML medium (...) is stable, equal in effectiveness as compared to Berenger's PML medium, while being more computationally efficient. (shrink)

This article accomplishes two closely connected things. First, it refutes an influential view about the relationship between perception and knowledge. In particular, it demonstrates that perceiving does not entail knowing. Second, it leverages that refutation to demonstrate that knowledge is not the most general factive propositional attitude.

I shall be mainly concerned with the question ‘What is personal propositional knowledge?’. This question is obviously quite narrowly focused, in three respects. In the first place, there is impersonal as well as personal knowledge. Second, a distinction is often drawn between propositional knowledge and practical knowledge. And third, as well as asking what knowledge is, it is also possible to ask whether and how knowledge of various kinds can be acquired: causal knowledge, a priori knowledge, moral knowledge, and so (...) on. I shall dwell briefly on each of these three points. First, there is the distinction between personal and impersonal knowledge – in other words, between the psychological concept of knowledge and the social one.1 We use the concept of knowledge to describe the cognitive condition of individuals; but we also use it to describe the progress of scientific and historical research. So for example we can speak or enquire about the state of knowledge in a particular field of biology or history. And if we do so, we are evidently not concerned with what anyone in particular knows about, say, the genetics of fruit flies or the career of Charlemagne, but rather with what the scientific or academic community knows. Needless to say, there is a close connection between personal and impersonal knowledge. But ‘It is known that p’ does not simply mean ‘Someone or other. (shrink)

This paper argues that we need to distinguish between two different ideas of a reason: first, the idea of a premise or assumption, from which a person’s action or deliberation can proceed; second, the idea of a fact by which a person can be guided, when he modifies his thought or behaviour in some way. It argues further that if we have the first idea in mind, one can act for the reason that p regardless of whether it is the (...) case that p , and regardless of whether one believes that p . But if we have the second idea in mind, one cannot act for the reason that p unless one knows that p . The last part of the paper briefly indicates how the second idea of a reason can contribute to a larger argument, showing that it is better to conceive of knowledge as a kind of ability than as a kind of belief. (shrink)

Hyman (1999, 2006) argues that knowledge is best conceived as a kind of ability: S knows that p iff S can φ for the reason that p. Hyman motivates this thesis by appealing to Gettier cases. I argue that it is counterexampled by a certain kind of Gettier case where the fact that p is a cause of the subject’s belief that p. One can φ for the reason that p even if one does not know that p. So knowledge (...) is not best conceived as an ability of this kind. (shrink)

In a 2010 article Turri puts forward some powerful considerations which suggest that Williamson's view of knowledge as the most general factive mental state is false. Turri claims that this view is false since it is false that if S sees that p, then S knows that p. Turri argues that there are cases in which (A) S sees that p but (B) S does not know that p. In response I offer linguistic evidence to suppose that in propositional contexts (...) “see” does not have the sort of meaning (a purely perceptual meaning) which would sustain Turri's claims about the cases he offers (specifically, the (A) verdicts). (shrink)

In this paper, I revisit the Davidsonian thesis that all reasons are causes. Drawing on a better taxonomy of reasons than the one Davidson provides, I argue that this thesis is either indefensible or uninteresting.

According to a number of recent philosophers, knowledge has an intimate relationship with rationality. Some philosophers hold, in particular, that rational agents do things for good motivating reasons, and that p can be one’s motivating reason for -ing (acting/believing/fearing/etc.) only if one knows that p. This paper argues against this view and in favor of the view that p cannot be one’s motivating reason for -ing—in the relevant sense—unless there is an appropriate explanatory connection between the fact that p and (...) one’s -ing. I argue that this view offers a better account of the cases alleged to support the knowledge view. (shrink)

A disjunctivist conception of acting for reasons is introduced by way of showing that a view of acting for reasons must give a place to knowledge. Two principal claims are made. 1. This conception has a rôle analogous to that of the disjunctive conception that John McDowell recommends in thinking about perception; and when the two disjunctivist conceptions are treated as counterparts, they can be shown to have work to do in combination. 2. This conception of acting for reasons safeguards (...) the connection between considerations that move us to act in particular ways and considerations that favour our acting in particular ways. (shrink)

The internalism-externalism debate is one of the oldest debates in epistemology. Internalists assert that the justification of our beliefs can only depend on facts internal to us, while externalists insist that justification can depend on additional, for example environmental, factors. Clayton Littlejohn proposes and defends a new strategy for resolving this debate. Focussing on the connections between practical and theoretical reason, he explores the question of whether the priority of the good to the right might be used to defend an (...) epistemological version of consequentialism, and proceeds to formulate a new 'deontological externalist' view. On this view, the justificatory status of a belief depends upon whether it is fit for the purposes of practical reasoning. Only beliefs that meet externalist standards are fit for such a purpose. If we want to understand how a wide range of norms (e.g., moral norms) apply to rational agents regardless of what their evidence or outlook is like, we have to embrace an externalist account of the justification. (shrink)