John W. Carroll

The possibility of continuous backwards time travel—time travel for which the traveler follows a continuous path through space between departure and arrival—gives rise to the double-occupancy problem. The trouble is that the time traveler seems bound to have to travel through his or her younger self as the trip begins. Dowe and Le Poidevin agree that this problem is solved by putting the traveler in motion for a gradual trip to the past. Le Poidevin goes on to argue, however, that the gradual trip gives rise to the Cheshire cat problem, a concern about whether the traveler survives the gradual trip. We address the Cheshire cat problem by proposing and considering new continuity constraints on identity over time. Along the way, we come upon an endurantist conception of temporal parts.

This chapter illustrates a theory that describes how certain modal statements, including counterfactual sentences, are dependent on context. Building on the work of Robert Stalnaker and David Lewis, its application to a familiar argument for fatalism and a recent exchange about time-traveler freedom between Kadri Vihvelin and Ted Sider is considered. This chapter presents a new perspective on the flaws and the seductiveness of both the fatalist argument and the freedom paradox. This new perspective may be applied to arguments for incompatibilism advanced by Carl Ginet and Peter van Inwagen. The issue of the compatibility of free will and determinism is generally regarded as one of the most serious metaphysical issues about human freedom. Consequence arguments of the sort made famous by Inwagen and Ginet are the leading arguments in favor of incompatibilism.

Ted Sider aptly and concisely states the self-visitation paradox thus: 'Suppose I travel back in time and stand in a room with my sitting 10-year-old self. I seem to be both sitting and standing, but how can that be?' (2001, 101). I will explore a relativist resolution of this paradox offered by, or on behalf of, endurantists.1 It maintains that the sitting and the standing are relative to the personal time or proper time of the time traveler and is intended to yield the result that Ted is sitting at a certain initial personal/proper time but is not standing relative to that time. Similarly, it is also supposed to yield that Ted is standing relative to a later personal/proper time, but not sitting relative to that..

The backward induction argument purports to show that rational and suitably informed players will defect throughout a finite sequence of prisoner's dilemmas. It is supposed to be a useful argument for predicting how rational players will behave in a variety of interesting decision situations. Here, I lay out a set of assumptions defining a class of finite sequences of prisoner's dilemmas. Given these assumptions, I suggest how it might appear that backward induction succeeds and why it is actually fallacious. Then, I go on to consider the consequences of adopting a stronger set of assumptions. Focusing my attention on stronger sets that, like the original, obey the informedness condition, I show that any supplementation of the original set that preserves informedness does so at the expense of forcing rational participants in prisoner's dilemma situations to have unexpected beliefs, ones that threaten the usefulness of backward induction.

A program for advancing a new philosophical account of physical laws is presented. The program is non-reductive in that it maintains that any correct account of physical laws must recognize law sentences as irreducible--that is, as not admitting of an analysis which does not invoke any unanalyzed nomic facts. The program has the unusual attraction of being consistent with Nominalism and epistemically in the spirit of Empiricism. ;Initially motivating my program is a two-stage attack in chapters two and three on all reductive accounts. The first stage of the attack is on traditional reductive accounts. Traditional reductive accounts are those accounts which do not invoke abstract entities in addressing nomic modality, i.e. in distinguishing universal laws from accidentally true generalizations or in explaining the relationship between statements of probability and statements of relative frequency. These accounts include those of Brian Skyrms, David Lewis, and Bas van Fraassen. The second stage of the attack is on all non-traditional reductive accounts. These accounts include David Armstrong's Nomic Realism. The two-stage attack exhausts the ontological ground for a reduction of laws. It is concluded that no reductive accounts of physical laws is possible. ;Chapter four spells out the details of my positive program. The program calls for statement of the basic philosophical truths about nomic modality, the specification of axiomatic principles governing physical laws, and the analysis of nomic facts in terms of other nomic facts. The basic truths about nomic modality are stated in full. Foremost among these is the Irreducibility Thesis which states that law sentences are irreducible. Some examples of axiomatic principles governing physical laws are specified and one example of an analysis of nomic facts in terms of other nomic facts is given. The analysis is of general causal statements. Time is also spent in chapter four critically reviewing other accounts in the history of philosophy which have recognized law sentences as irreducible. ;The final chapter addresses the most common and the most significant objection to my positive program. That objection is the epistemological challenge of Empiricism. I argue that my program and, in particular, the Irreducibility Thesis are epistemologically innocuous.

An enticing view about explanation consists of two theses. First, there is the Relevance Thesis, the thesis that the truth of explanation sentences depends on a contextually selected relevance relation. The idea is that whether an utterance is true depends on what factors the context counts as relevant. Second, there is the Contrastivity Thesis, the thesis that the truth of explanation sentences depends on a contextually determined contrastive focus. This metalinguistic view is enticing, and elements of it have been defended by van Fraassen, Woodward, Schaffer, and others. Nevertheless, the enticing view is flawed; both the Contrastivity Thesis and the Relevance Thesis are mistaken.

The self-visitation paradox is one paradox of time travel. As Ted Sider puts it, “Suppose I travel back in time and stand in a room with my sitting 10-year-old self. I seem to be both sitting and standing, but how can that be?” (2001, 101). So as not to beg any questions, let us label what is sitting B and what is standing C. The worry is about how B can be C in light of the looming contradiction that this one person would be sitting and standing. Sider’s own approach is perdurantist, and holds that B is not C. My concern, though, is with solutions offered by, or on behalf of, endurantists–more 1 specifically, with solutions holding that B is C. The endurantist answer I shall criticize is a relativizer position maintaining that the sitting and the standing need to be relativized to the personal time or proper time of the time traveler. This manner of solution has been offered by Paul Horwich (1975, 433-435 ; 1987, 114-115) and also by Simon Keller and Michael Nelson (2001, 344). I will show that such a view has a linguistically suspect element and that there are three further reasons why relativizing only in this way falls short of solving the paradox. This will be enough to squash the relativizer position because it will not be clear how additional relativization could help, and furthermore any additional relativization would only make the linguistic matter worse. I will also present some considerations in favor of a non-contradiction endurantist alternative; this view eliminates the need for any relativization by denying that sitting and standing are contradictory properties.

ConclusionIn conclusion, I shall indicate one consequence of (3.4). The major resultof work on infinitely iterated Prisoner's Dilemma games is that there existcooperative equilibria in such games. I have suggested above that myaccount of finitely, but indefinitely, iterated Prisoner's Dilemma gamesreflects the nature of genuine iterated Prisoner's Dilemmas more accu-rately than accounts involving infinite iterations. If my suggestion iscorrect, then one consequence of (3.4) - of there being only uncooperativeequilibria in finitely, but indefinitely, iterated games - is to call intoquestion the significance of the existence of cooperative equilibria ininfinitely iterated Prisoner's Dilemma games.

From an Ontological Point of View is a highly original and accessible exploration of fundamental questions about what there is. John Heil discusses such issues as whether the world includes levels of reality; the nature of objects and properties; the demands of realism; what makes things true; qualities, powers, and the relation these bear to one another. He advances an account of the fundamental constituents of the world around us, and applies this account to problems that have plagued recent work in the philosophy of mind and metaphysics (color, intentionality, and the nature of consciousness)

Some scientists try to discover and report laws of nature. And, they do so with success. There are many principles that were for a long time thought to be laws that turned out to be useful approximations, like Newton’s gravitational principle. There are others that were thought to be laws and still are considered laws, like Einstein’s principle that no signals travel faster than light. Laws of nature are not just important to scientists. They are also of great interest to us philosophers, though primarily in an ancillary way. Qua philosophers, we do not try to discover what the laws are. We care about what it is to be a law, about lawhood, the essential difference between something’s being a law and something’s not being a law. It is one of our jobs to understand lawhood and convey our understanding to others.