The Attribute-Neutral Foundations of Spinoza’s Physics

Alison Peterman

University of Rochester

The most fundamental principles of Cartesian physics make reference to extension and motion. These have no counterparts in minds and it seems we cannot learn anything about minds by considering them. For example, the distinction between bodies is determined by their relative motion and their mutual interaction is governed by the conservation of total quantity of motion. It is hard to see how such principles of individuation and collision could help us understand the individuation of minds or their causal powers. Yet Spinoza famously argues at IIP7 of the Ethics that ‘the order and connection of ideas is the same as the order and connection of things’. This suggests that minds are related to minds in similar ways that bodies are related to bodies, or that the structural features of the mental and the physical world are isomorphic. So we might expect, for example, that what individuates particular things, and what constitutes causal interaction between those things, to be identical or analogous in the mental world and the physical world. Let’s assume that these structural features are identical (Spinoza does say after all that the order and connection is the same, idem). These structural principles should not invoke any specifically physical properties like extension and motion. So to the extent that physics for Spinoza is in some sense concerned with the structure of the physical world, we should expect it to be concerned with ‘attribute-neutral’ structural principles. If this is right, then we are presented with a unique and interesting constraint on any account that Spinoza can offer of bodies and their motions. There is strong evidence that Spinoza does aim to ground proofs of physical doctrines (like the laws of impact) on such principles. In this paper, I discuss several of these principles and trace their use to Spinoza’s most thorough engagements with physics: the Principles of Cartesian Philosophy and the ‘physical interlude’ following IIP13 of the Ethics. In the latter, Spinoza is very concerned to develop one such principle – the criterion of identity for a complex individual. Indeed, the physical interlude is largely aimed at articulating attribute-neutral criteria of identity for complex things. This is unsurprising when we consider its stated goal is to find those very features of bodies which can be fruitfully applied to the study of minds. But I am primarily concerned to trace and explore the instances where Spinoza is compelled to modify Descartes’ original proofs in order to ground them upon (un-Cartesian) attribute-neutral principles. In particular we find him deploying a principle of non-contrariety for objects in general, along with what Alan Gabbey has called the ‘principle of least modal mutation’, in order to avoid relying on the principle of the conservation of quantity of motion (which is not attribute-neutral) in the proofs of certain key propositions. This project intersects in several ways with the other three symposium papers since it has implications for Spinoza’s attitude to mathematization, the role of motion in individuation, and the attribute-neutral status of conatus.