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My research is focused on questions of theory interpretation and equivalence. Physics purports to present us with accounts of what the world is fundamentally like, accounts that are sometimes strikingly at odds with our everyday conceptions and experiences. Yet scientific theories are often presented in mathematical terms that seem altogether disconnected from the physical world. So how is it that we get from these elaborate mathematical structures to esoteric and radical accounts of what the physical world is ultimately like? In what ways do the mathematical structures and equations guide us, and in what ways might they actually mislead us or lend themselves to competing physical pictures? Is it ever correct to understand radically different mathematical formalisms as physically equivalent—as representing the same underlying physical content? If so, when? What are the principles that guide us in the transition from mathematical characterizations to physical descriptions of the world? These are some of the central questions guiding my research, both in general and as applied to specific physical theories (for example, Newtonian gravitation theory and special relativity).


Coffey, Kevin. 2014. “Theoretical Equivalence as Interpretive Equivalence”. The British Journal for the Philosophy of Science 65 (4): 821–844. (

Abstract: The problem of theoretical equivalence is traditionally understood as the problem of specifying when superficially dissimilar accounts of the world are reformulations of a single underlying theory. One important strategy for answering this question has been to appeal to formal relations between theoretical structures. This article presents two reasons to think that such an approach will be unsuccessful and suggests an alternative account of theoretical equivalence, based on the notion of interpretive equivalence, in which the problem is merely an instance of a broader problem in the philosophy of physics. I thus conclude that there is no distinctive problem of theoretical equivalence at all. Two difficulties my approach raises for realist replies to the threat of underdetermination are then discussed, with particular emphasis on a recent reply by Norton.

Coffey, Kevin. 2020. “On the Ontology of Particle Mass and Energy in Special Relativity”. Synthese. (

Abstract: Einstein claimed that the fundamental dynamical insight of special relativity was the equivalence of mass and energy. I disagree. Not only are mass and energy not equivalent (whatever exactly that means) but talk of such equivalence obscures the real dynamical insight of special relativity, which concerns the nature of 4-forces and interactions more generally. In this paper I present and defend a new ontology of special relativistic particle dynamics that makes this insight perspicuous and I explain how alleged cases of mass-energy conversion can be accommodated within that ontology.


Coffey, Kevin. 2021. “(Competing?) Formulations of Newtonian Gravitation: Reflections at the Intersection of Interpretation, Methodology, and Equivalence”. Journal of Philosophy. (forthcoming)

Abstract: It is sometimes said there are two ways of formulating Newtonian gravitation theory. On the first, matter gives rise to a gravitational field deflecting bodies from inertial motion within flat spacetime. On the second, matter’s accelerative effects are encoded in dynamical spacetime structure exhibiting curvature and the field is ‘geometrized away’. Are these two accounts of Newtonian gravitation theoretically equivalent? Conventional wisdom within the philosophy of physics is that they are, and recently several philosophers have made this claim explicit. In this paper I develop an alternative approach to Newtonian gravitation on which the equivalence claim fails, and in the process identify an important but largely overlooked consideration for interpreting physical theories. I then apply this analysis to (a) put limits on the uses of Newtonian gravitation within the methodology of science, and (b) defend the interpretive approach to theoretical equivalence against formal approaches, including the recently popular criterion of categorical equivalence.

Coffey, Kevin. 2021. “Symmetry and Interpretation in Newtonian Gravitation: The Importance of Interaction(s)”. (under review)

Abstract: Newtonian gravitation theory is often claimed to exhibit an important symmetry with respect to its inertial structure, a symmetry that allows one to draw the distinction between inertial structure and gravitational field in indefinitely many ways. Philosophers of physics have used this fact to conclude that both features ought to be interpreted as gauge quantities—as conventional choices without underlying physical significance—and thus that there really are no gravitational fields posited by the theory. This paper provides a counterpoint to this view: I defend the postulation of a genuine distinction between inertial structure and gravitational field. Along the way I argue that, despite current consensus, Newtonian cosmology really is inconsistent. These claims are then marshaled in support of a broader lesson regarding the relationship between symmetry considerations and theory interpretation.

Coffey, Kevin. 2021. “Equivalence and Interpretive Fundamentality in Classical Mechanics”.

Abstract: When there are theoretically equivalent formulations of a theory possessing radically different mathematical structures, which formulation is relevant for determining the ontology of the theory? I explore this question through the lens of one particular case: the Newtonian and Lagrangian formulations of classical mechanics. I argue that the Newtonian formulation is fundamental, and defend that claim against recent arguments by Jill North for Lagrangian fundamentality. In the process, I make explicit a host of considerations that are largely implicit within our interpretive practices. The paper thus functions both as an inquiry into classical mechanics, and as a case study concerning the general nature of interpretive principles.


Coffey, Kevin. 2021. “Is Underdetermination a Problem for Structural Realism?”.

Abstract: Enthusiasm for scientific realism is often tempered by considerations of theory underdetermination: that is, the challenge of justifying belief in a particular theory when there are (or likely are) alternative theories equally adequate to the empirical data. Recently, however, several philosophers have argued that (epistemic) structural realism is insulated from the threat of underdetermination in a way that other, standard forms of scientific realism are not. (Structure realism is the view, very roughly, that we ought to commit ourselves only to the physical structures represented in our best theories, not the ontologies of entities and properties that constitute the relata in those theories.) For the problem of underdetermination turns on the claim that the realist is confronted with competing sets of commitments (e.g., competing theories) that are equally able to account for the empirical data. But the commitments of the structural realist only include physical structures, not the underlying theoretical ontologies. On this basis structural realists have argued that many (alleged) instances of theoretically equivalent rival theories are actually instantiations of the same underlying physical structures, despite their differing ontologies, and thus do not count as genuine competitors, at least not for the structural realist; they only count as genuine competitors according to the commitments of standard realism. Structural realism thus appears to defuse the threat of underdetermination that plagues other forms of scientific realism.


I argue here that the opposite is true, even granting the structural realist’s strategy. By retreating to structure, the structural realist avoids one form of underdetermination only at the cost of exposing herself to another form of underdetermination—‘structural underdetermination’—which doesn’t pose a problem for standard realism. This new form of underdetermination arises on account of the fact that, in eschewing interpretive claims of underlying ontology, the structural realist is no longer able to identify superficially different structural representations that are, intuitively, equivalent (i.e., that are reformulations of one another). This presents the structural realist with cases of underdetermination that simply do not arise for the standard realist. Moreover, unlike more traditional forms of underdetermination, the ubiquity of which is controversial, there are reasons to think that structural underdetermination is widespread. In this sense, then, I argue that the problem of underdetermination is actually worse for the structural realist than it is for the standard realist.

This argument brings to the surface a question that has dogged structural realism at least since John Worrall introduced the term: namely, what is meant by ‘structure’? For one natural way in which the structural realist might reply is to argue that theoretically equivalent formulations with superficially different structures actually do exhibit the same underlying structure. But the plausibility of this claim requires that the structural realist say much more about the notion of structure that’s operative in her account. I argue that the widespread Ramsey-sentence approach to theory structure, for example, isn’t able to make the sort of discriminations needed to defuse many cases of structural underdetermination. I conclude by arguing that recent attempts to redefine the relevant notion of structure fail to appreciate how structural underdetermination arises, and thus are unlikely to provide an adequate resolution of the problem.

“Scientific Realism and the Unconceived”


“Realism, Theory Dependence, and Maxwell’s Lagrangian Methodology”


“Can the Realist Be Agnostic about Quantum Theory?"

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