David Marr's theory of vision has been widely cited by philosophers and psychologists. I have three projects in this paper. First, I try to offer a perspicuous characterization of Marr's theory. Next, I consider the implications of Marr's work for some currently popular philosophies of psychology, specifically, the “hegemony of neurophysiology view”, the theories of Jerry Fodor, Daniel Dennett, and Stephen Stich, and the view that perception is permeated by belief. In the last section, I consider what the phenomenon of vision must be like for Marr's project to succeed.

The commensurability of two theories can be defined (relative to a given set of questions) as the ratio of the total information of their shared answers to the total information of the answers yielded by the two theories combined. Answers should be understood here as model consequences (in the sense of the author's earlier papers), not deductive consequences. This definition is relative to a given model of the joint language of the theories, but can be generalized to sets of models. It turns out to capture also the idea of incommensurability as conceptual alienation. Incommensurability so defined does not imply incomparability.

There is sufficient evidence at present to justify the belief that the universe began to exist without being caused to do so. This evidence includes the Hawking-Penrose singularity theorems that are based on Einstein's General Theory of Relativity, and the recently introduced Quantum Cosmological Models of the early universe. The singularity theorems lead to an explication of the beginning of the universe that involves the notion of a Big Bang singularity, and the Quantum Cosmological Models represent the beginning largely in terms of the notion of a vacuum fluctuation. Theories that represent the universe as infinitely old or as caused to begin are shown to be at odds with or at least unsupported by these and other current cosmological notions.

Professor Grünbaum's much-discussed refutation of Zeno's metrical paradox turns out to be ad hoc upon close examination of the relevant portion of measure theory. Although the modern theory of measure is able to defuse Zeno's reasoning, it is not capable of refuting Zeno in the sense of showing his error. I explain why the paradox is not refutable and argue that it is consequently more than a mere sophism.

Benton Stidd has defended the position that punctuationists are not wrong about the inadequacy of the synthetic theory of evolution for explaining evolution. The thrust of his defense is that arguments to the contrary by Thompson (1983a) involve a rational reconstruction along logical empiricist lines, which is insensitive to historical and social forces in a way that the Kuhnian Weltanschauung view that he espouses is not. I argue in this paper that Stidd has entirely misunderstood my arguments, that the soundness of my arguments does not depend on acceptance of logical empiricism (they are just as sound on a Kuhnian view), and that Stidd fails to establish that punctuated equilibria is a new “paradigm“.

It is argued that Galileo's theory of justification was a version of explanationism. Galileo's Dialogue on the Two Chief World Systems is to be read as primarily a defense of his theory of the tides. He shows how, by assuming Copernican motions, he can explain the tides, thereby justifying the endorsement of Copernicus. The crux of the argument rests on Galileo's account of explanation, which is novel in its reliance on the use of geometry. Finally, the consequences of his use of geometry, and his views on the limits of knowledge, force us to conclude that if Galileo was a realist, his realism was so highly constrained as to be irrelevant.

I argue that post-Kuhnian approaches to rational scientific change fail to appreciate several distinct philosophical requirements and relativist challenges that have been assumed to be, and may in fact be essential to any adequate conception of scientific rationality. These separate requirements and relativist challenges are clearly distinguished and motivated. My argument then focuses on Shapere's view that there are typically good reasons for scientific change. I argue: (1) that contrary to his central aim, his account of good reasons ultimately presupposes the requirement of universal standards of scientific reasoning; (2) that the good reasons established by his account underdetermine the rationality of scientific change and allow that other changes would have been equally or even more rational; (3) that as a result, Shapere's approach fails to meet what I characterize as the challenges of moderate, sociological, and cognitive relativism.

The chief objections raised by Doppelt (this issue, “The Philosophical Requirements for an Adequate Conception of Scientific Rationality“) against my views fall into three groups: ones having to do with my concept of “success” (that I have provided no analysis of it, and that therefore my concept of “reason“ in science is likewise unexplained; that it requires appeal to some universal criterion); ones having to do with the role of standards or criteria in science (how they are related to substantive beliefs; the possibility of rejecting them); and ones purporting to show that I have not escaped relativism (underdetermination of beliefs; problem of loss in scientific change). I reply to each of these groups of criticisms in turn, concluding with some remarks on the status and validity of the requirements he lays down for any account of scientific rationality.

Classic studies of explanation, such as those of Hempel and Bromberger, took it for granted that an explanation-seeking question of the form “Why P?“ should be understood as asking about the proposition P. This view has been recently challenged by Bas van Fraassen and Alan Garfinkel. They acknowledge that some questions have the surface form “Why P?” but they hold that a correct reading for why-questions should take the form “Why P (rather than Q)?”, where Q is a contrasting alternative. This contrast theory is discussed here. It is argued that, properly understood, the contrast theory and the propositional approach can and should give equivalent readings to why-questions.