The possibility of time travel, as permitted in General Relativity, is responsible for constraining physical fields beyond what laws of nature would otherwise require. In the special case where time travel is limited to a single object returning to the past and interacting with itself, consistency constraints can be avoided if the dynamics is continuous and the object's state space satisfies a certain topological requirement: that all null-homotopic mappings from the state-space to itself have some fixed point. Where consistency constraints do exist, no new physics is needed to enforce them. One needs only to accept certain global topological constraints as laws, something that is reasonable in any case.

In the preface to the Principia (1687) Newton famously states that “geometry is founded on mechanical practice.” Several commentators have taken this and similar remarks as an indication that Newton was firmly situated in the constructivist tradition of geometry that was prevalent in the seventeenth century. By drawing on a selection of Newton's unpublished texts, I hope to show the faults of such an interpretation. In these texts, Newton not only rejects the constructivism that took its birth in Descartes's Géométrie (1637); he also presents the science of geometry as being more powerful than his Principia remarks may lead us to believe.

This paper addresses a central interpretive problem in understanding Pierre Duhem's philosophy of science. The problem arises because there is textual support for both realist and antirealist readings of his work. I argue that his realist and antirealist claims are different. For Duhem, scientific reasoning leads straight to antirealism. But intuition (reasons of the heart) motivates, without justifying, a kind of realism. I develop this idea to suggest a motivational realist interpretation of Duhem's philosophy.

Francis Bacon (1561–1626) wrote that good scientists are not like ants (mindlessly gathering data) or spiders (spinning empty theories). Instead, they are like bees, transforming nature into a nourishing product. This essay examines Bacon's “middle way” by elucidating the means he proposes to turn experience and insight into understanding. The human intellect relies on “machines” to extend perceptual limits, check impulsive imaginations, and reveal nature's latent causal structure, or “forms.” This constructivist interpretation is not intended to supplant inductivist or experimentalist interpretations, but is designed to explicate Bacon's account of science as a collaborative project with several interdependent methodological goals.

Recent defenses of a priori knowledge can be applied to the idea of conventions in science in order to indicate one important sense in which conventionalism is correct—some elements of physical theory have a unique epistemological status as a functionally a priori part of our physical theory. I will argue that the former a priori should be treated as empirical in a very abstract sense, but still conventional. Though actually coming closer to the Quinean position than recent defenses of a priori knowledge, the picture of science developed here is very different from that developed in Quinean holism in that categories of knowledge can be differentiated.

Biological research on race has often been seen as motivated by or lending credence to underlying racist attitudes; in part for this reason, recently philosophers and biologists have gone through great pains to essentially deny the existence of biological human races. We argue that human races, in the biological sense of local populations adapted to particular environments, do in fact exist; such races are best understood through the common ecological concept of ecotypes. However, human ecotypic races do not in general correspond with ‘folk’ racial categories, largely because many similar ecotypes have multiple independent origins. Consequently, while human natural races exist, they have little or nothing in common with ‘folk’ races.

Race is a prominent category in medicine. Epidemiologists describe how rates of morbidity and mortality vary with race, and doctors consider the race of their patients when deciding whether to test them for sickle-cell anemia or what drug to use to treat their hypertension. At the same time, critics of racial classification say that race is not real but only an illusion or that race is scientifically meaningless. In this paper, I explain how race is used in medicine as a proxy for genes that encode drug metabolizing enzymes and how a proper understanding of race calls into doubt the practice of treating race as a marker of any medically relevant genetic trait.

I argue here that critics of biological explanations of human nature are mistaken when they maintain that the truth of genetic determinism implies the end of critical evaluation and reform of our social institutions. Such a claim erroneously presupposes that our social values, practices, and institutions have nothing to do with what makes biological explanations troublesome. What constitutes a problem for those who are concerned with social justice is not the fact that particular behaviors might be genetically determined, but the fact that our value system and social institutions create the conditions that make such behaviors problematic.

Experimental “localism” stresses the importance of context-specific knowledge, and the limitations of universal theories in science. I illustrate Latour's radical approach to localism and show that it has some unpalatable consequences, in particular the suggestion that problems of external validity (or how to generalize experimental results to nonlaboratory circumstances) cannot be solved. In the last part of the paper I try to sketch a solution to the problem of external validity by extending Mayo's error-probabilistic approach.

There is good reason to suppose that our best physical theories are false: In addition to its own internal problems, the standard formulation of quantum mechanics is logically incompatible with special relativity. I will also argue that we have no concrete idea what it means to claim that these theories are approximately true.

This paper aims at answering the simple question, “What is spontaneous symmetry breaking (SSB) in classical systems?” I attempt to do this by analyzing from a philosophical perspective a simple classical model which exhibits some of the main features of SSB. Related questions include: What does it mean to say that a symmetry is spontaneously broken? Is it broken without any causes, or is the symmetry not broken but merely hidden? Is the principle, “no asymmetry in, no asymmetry out,” violated by SSB? What really distinguishes SSB from the usual types of symmetry breaking?

Recently, Brukner and Zeilinger have presented a number of arguments suggesting that the Shannon information is not well defined as a measure of information in quantum mechanics. If established, this result would be highly significant, as the Shannon information is fundamental to the way we think about information not only in classical but also in quantum information theory. On consideration, however, these arguments are found unsuccessful; I go on to suggest how they might be arising as a consequence of Zeilinger's proposed foundational principle for quantum mechanics.

This paper examines some common measures of complexity, structure, and information, with an eye toward understanding the extent to which complexity or information-content may be regarded as objective properties of individual objects. A form of contextual objectivity is proposed which renders the measures objective, and which largely resolves the puzzle of Maxwell's Demon.

If two theory formulations are merely different expressions of the same theory, then any problem of choosing between them cannot be due to the underdetermination of theories by data. So one might suspect that we need to be able to tell distinct theories from mere alternate formulations before we can say anything substantive about underdetermination, that we need to solve the problem of identical rivals before addressing the problem of underdetermination. Here I consider two possible solutions: Quine proposes that we call two theories identical if they are equivalent under a reconstrual of predicates, but this would mishandle important cases. Another proposal is to defer to the particular judgements of actual scientists. Consideration of an historical episode—the alleged equivalence of wave and matrix mechanics—shows that this second proposal also fails. Nevertheless, I suggest, the original suspicion is wrong; there are ways to enquire into underdetermination without having solved the problem of identical rivals.

I discuss the behavior of the Akaike Information Criterion in the limit when the sample size grows. I show the falsity of the claim made recently by Stanley Mulaik in Philosophy of Science that AIC would not distinguish between saturated and other correct factor analytic models in this limit. I explain the meaning and demonstrate the validity of the familiar, more moderate criticism that AIC is not a consistent estimator of the number of parameters of the smallest correct model. I also give a short explanation why this feature of AIC is compatible with the motives for using it.

Reverse engineering is a matter of inferring adaptive function from structure. The utility of reverse engineering for evolutionary biology has been a matter of controversy. I offer a simple taxonomy of the uses of engineering design in assessing adaptation, with a variety of illustrations. The plausibility of applications of engineering design reflects the specific way the models are elaborated and derived.

Recent years have seen increased interest in the question of whether it is possible to provide an evolutionary game-theoretic explanation for certain kinds of social norms. I sketch a proof of a general representation theorem for a large class of evolutionary game-theoretic models played on a social network, in hope that this will contribute to a greater understanding of the long-term evolutionary dynamics of such models, and hence the evolution of social norms.

Marc Ereshefsky argues that pluralism about species suggests that the species concept is not theoretically useful. It is to be abandoned in favor of several concrete species concepts that denote real categories. While accepting species pluralism, the present paper rejects eliminativism about the species category. Based on the idea that the species concept is a so-called investigative kind concept, it is argued that the species concept is important and that it is possible to make sense of a general species concept despite the existence of different concrete species concepts.

The ubiquitous probabilities of evolutionary theory (ET) spark the question: Which interpretation of probability is the most appropriate for ET? There is reason to think that, whatever we take probabilities in ET to be, they must be consistent with both determinism and indeterminism. I argue that the probabilities used in ET are objective in a realist sense, if not in an indeterministic sense. Furthermore, there are a number of interpretations of probability that are objective and would be consistent with deterministic evolution and indeterministic evolution. However, I suggest that evolutionary probabilities are best understood as propensities of population-level kinds.

If a classical system has infinitely many degrees of freedom, its Hamiltonian quantization need not be unique up to unitary equivalence. I sketch different approaches (Hilbert space and algebraic) to understanding the content of quantum theories in light of this non-uniqueness, and suggest that neither approach suffices to support explanatory aspirations encountered in the thermodynamic limit of quantum statistical mechanics.