I defend a formulation of the Ramsey Test with a condition for accepting negations of conditionals. It is implicit in the assumptions of the triviality theorems of Gärdenfors, Harper, and Lewis; and it allows for a unified proof of those theorems, from weaker assumptions about belief revision. This leads to a proof of McGee's thesis that iterated conditionals do not obey modus ponens.

This essay is a philosophical evaluation of some of the findings of Wald and Penrose in which they claim to have supported an arrow (or the irreversibility) of time in quantum gravity. First, the notion of lawlike irreversibility (or anisotropy) of time is spelled out, then the general situation in quantum mechanics is briefly discussed. Finally, the findings in quantum gravity are evaluated against such a background. My conclusion is that the arrow of time found in quantum gravity is at best de facto (nonlawlike).

History of Science is a many-sided subject, permitting approach from the point of view of various human interests, and presenting a wide variety of problems, many of them paradoxical and perhaps not capable of satisfactory solution. In the following it will probably seem to the reader a number of times that I am talking at cross purposes. Anything that I can say is of necessity limited by my background as a physicist.

The purported failures of ergodic theory (seen in its often proved ineptitude to ground a mechanical explanation of thermodynamics) are shown to arise from misconception of the functions served by scientific explanation. In fact, the predictive failures of ergodic theory are precisely its points of greatest physical utility, where genuinely new knowledge about actual physical systems can be obtained, once the links between explanation and reconstructive estimation are recognized.

There is no set Δ of probability axioms that meets the following three desiderata:

• (1) Δ is vindicated by a Dutch book theorem;

• (2) Δ does not imply regularity (and thus allows, among other things, updating by conditionalization);

• (3) Δ constrains the conditional probability q(·, z) even when the unconditional probability p(z) (= q(z, T)) equals 0.

• This has significant consequences for Bayesian epistemology, some of which are discussed.

R. Laudan and L. Laudan (1989) have put forth a new model intended to solve the problem of disagreement, the problem of consensus, and the problem of innovation in science. In support of this model they cite the history of the acceptance of continental drift, or plate tectonics. In this discussion, I claim that this episode does not constitute an instance of their model. The historical evidence does not support this model. Indeed, closer examination seems to weaken it. I also sketch an alternative model.

In 1924, Bohr, Kramers and Slater tried to introduce into microphysics conservation principles that hold only on the average. This attempt was abandoned in the light of the Compton-Simon experiment (and its later refinements). Since that time, except for a moment of doubt in 1936, it has been thought that the classical conservation laws (for energy and momentum) hold in quantum theory for each individual interaction, in a way that yields the classical exchange-and-balance of momentum (or energy) familiar from the laws of elastic collisions. It has been thought, that is, that in each individual “collision” what one part of the total system loses in linear momentum (say) another part gains, so as to maintain the same total amount afterwards as before. To those familiar with discussions of the interpretation of quantum theory, however, it will be apparent that the very concepts needed to express this idea of an elastic collision are generally not admitted in the theory. For one needs the idea that both before and after collision the total system has a well-defined value for the conserved quantity and, moreover, that the various component parts of the system have well-defined values for those quantities out of which the conserved one is composed. But in the case of spin, for example, it is customary to say that although total spin may be conserved in certain interactions one cannot attribute values to the separate components of spin (in various directions) because the associated operators do not commute. (Thus the whole sum is not even the sum of its parts.) Moreover, one does not generally refer to the values of quantities except in eigenstates. Hence, in general, one would not refer to the value of the conserved quantity before and after interaction, except for interactions initiated in eigenstates.

It is widely held that (1) there are autonomous levels of organization above that of the macromolecule and that (2) at least sometimes macromolecular processes are best explained in terms of such autonomous kinds. I argue that molecular developmental biology honors neither of these claims, and I show that the only way they can be rendered consistent with a minimal physicalism is through the adoption of controversial claims about causation and explanation which undercut the force of these two antireductionism claims.

The year 1897 saw the publication of the first of the modern logical paradoxes. It was published by Cesare Burali-Forti, the Italian mathematician whose name it has come to bear. Burali-Forti's own formulation of the paradox was not altogether satisfactory, as he had confused well-ordered sets as defined by Cantor with what he himself called “perfectly ordered sets” (“Classe parfettamente ordinata”). However, he soon realized his mistake, and published a note admitting the error and making the correction. He concluded the note with the observation that his result could be established on the basis of the correct definition of well-ordered set as easily as for the “perfectly ordered sets” for which it had first been obtained. We shall reproduce his results in their corrected form.

1. Objective of the Paper. This is an exercise in formalism; an attempt to see what a certain hypothesis would look like if it were spelled out in more detail than it has so far received. The object is to frame a self-consistent hypothesis that includes certain contributions of both optimism and pessimism. We would like to save the moral advantages of each position; at first glance they seem logically exclusive.

I discuss Earman's program to achieve an objective account of the Higgs mechanism within the C∗ algebraic approach to quantum field theory. Pointing to three results obtained within this approach, I argue that if one follows Earman and understands the Higgs mechanism as a constraint, it appears to be a genuine quantum phenomenon that does not simply arise through the correspondence principle. This casts further this casts doubts on the validity of the Dirac conjecture that identifies first-class constraints and gauge transformations and that provides a major motivation for both Earman's program and Struyve's demonstration that a gauge-invariant account of the Higgs mechanism can be accomplished at the classical level.

In this paper, I offer a new defense of scientific realism, tailored for the Akaikean paradigm of statistical hypothesis testing. After proposing definitions of verisimilitude and predictive success, I use computer simulations to show how the latter depends on the former, even in the kind of case featured in a recent argument for instrumentalism.

In his article “Reflexive Predictions” in a recent issue of this Journal [1], Professor Roger C. Buck refers to our theorem concerning correct public prediction of economic and, in general, social events [2]. Unfortunately he misunderstands the nature of our theorem. He begins by stipulating the infinite regress which originally led to the belief that correct public prediction in the social sciences might be impossible: the forecaster who attempts to take into account the agent's reaction to his public prediction, finds his adjusted public prediction again falsified by the agent's reaction to it, and so on ad infinitum [3]. Professor Buck then makes an admittedly tempting mistake. He argues that, provided the sequence of public predictions—each one adjusted for the agent's reaction to its predecessor—converges towards some value, correct public prediction is possible: at the end of a sequence of falsified predictions the forecaster, as it were, catches up with the agent.

Entropy is proposed as a concept which in its broader scope can contribute to the study of the General Information System. This paper attempts to identify a few fundamental subconcepts and lemmas which will serve to facilitate further study of system order. The paper discusses: partitioning order into logical and arbitrary kinds; the relationship of order to pattern; and suggested approaches to evaluating and improving the General Information System.

Recent proposals that the substrate of memory is molecular raise questions about where this molecular model stands in relation to the dominant synaptic model of memory. In this article, we address the perceived rivalry between these models and ask whether they can be integrated. We argue that addressing rivalry or integration requires delineating the explananda of synaptic and molecular models, as well as revisiting assumptions about how these models account for their explananda. The perceived rivalry between these models exemplifies epistemic costs that arise when we try to pit explanatory models as rivals or integrate them.

In what follows, I critique the interpretation that Sober and Wilson offer of their group selection model in Unto Others. Sober and Wilson mistakenly claim that their model operates as an example of Simpson's paradox and defend an interpretation of their model according to which groups are operated upon by natural selection. In the place of their interpretation, I offer one that parallels the mathematical calculation of the model's outcome and does not depend on the postulation of a force of group selection or a value for group fitness.