Eliminating Modality from the Determinism Debate? Models vs. Equations of Physical Theories

This paper addresses a specific question of reductionism, viz., the question of whether modalities are basic for the notions of determinism and indeterminism, or whether one can do without them. I will argue that the current treatment of these notions within philosophy of science, which takes determinism and indeterminism to be properties of scientific theories rather than metaphysical theses about what the world is like, amounts to a reductionist stance with respect to modality for which no good reasons have been given. Furthermore, I will show that the current implementation of that treatment is not without problems: there is a discrepancy between the official definition of determinism and indeterminism, phrased in terms of the ‘modally flat’ collection of models of a theory, and the practice of assessing determinism by looking at the possibly branching space of solutions to a theory’s constitutive equations, which moves that practice much closer to a pro-modality stance. Apart from commenting on use of models vs. equations in the determinism debate within philosophy of science, my paper is also an attempt at getting clear on the proper dialectics of the question of modal reductionism. I will thus also lay out my view as to how determinism and indeterminism or other modal notions should be addressed.