This project coalesces around a simple but highly counterintuitive claim forcefully emphasized by the 17th century Dutch rationalist, Baruch Spinoza. Following others, I call it the explanatory barrier between the attributes (EB), and I suspect it may be true. My aims here are far more modest than establishing the EB’s truth, however, for fairly strong critical consensus in Spinoza scholarship suggests that Spinoza did not have, and that there really could not really be, any good reason for believing it. That claim is certainly false, in both respects. This project is my attempt to uncover what Spinoza’s reasons might have been and to show that they are compelling.
The explanatory barrier between the attributes is the thesis that there are no causal or explanatory connections between the mental and the physical. Actually, it is broader than this, but this framing is a reasonable place to start. In what follows, I establish the centrality of the explanatory barrier within Spinoza’s overall metaphysics. I argue that Spinoza responds not directly to traditional Cartesian skepticism, but to a related, and more interesting explanatory problem previously unappreciated by his commentators. I show this by giving a new reading of Spinoza’s Short Treatise that reconstructs an argument for the EB as a response to this problem. Spinoza thinks the explanatory barrier’s truth provides the best explanation for our causal knowledge in ordinary cases. Said differently, the explanatory barrier is the best response to a class of skeptical or explanatory problems that appear intractable if the EB is not true.
The dissertation’s latter half uses this argument to defend what I call Spinozistic Isolationism: Spinozism, plus a compelling justification for the EB. I claim that Isolationism strongly undermines interactionist dualism, accommodates the best arguments for physicalism while retaining key advantages over it, and can be interpreted as either a form of or very nearby rival to Russellian panpsychism. I think the argument given here for the explanatory barrier helps justify Spinoza’s basic metaphysical project. So justified, Isolationism deserves serious consideration as the most compelling route towards resolving longstanding debates in the metaphysics of mind.