From the logic of ideas to active-matter materialism: Priestley’s Lockean problem and early neurophilosophy

Empiricism is a claim about the contents of the mind: its classic slogan is nihil est in intellectu quod non fuerit in sensu, “there is nothing in the mind (intellect, understanding) which is not first in the senses.” As such, it is not a claim about the fundamental nature of the world as material. I focus here on in an instance of what one might term the materialist appropriation of empiricism. One major component in the transition from a purely epistemological claim about the mind and its contents to an ontological claim about the nature of the world is the new focus on brain–mind relations in the eighteenth century. Here I examine a Lockean trajectory as exemplified in Joseph Priestley’s 1777 Disquisitions Relating to Matter and Spirit. However, Locke explicitly ruled out that his inquiry into the logic of ideas amounted to a “physical consideration of the mind.” What does it mean, then, for Priestley to present himself as continuing a Lockean tradition, while presenting mental processes as tightly identified with “an organical structure such as that of the brain” (although he was not making a strict identity claim as we might understand it, post-Smart and Armstrong)? One issue here is that of Priestley’s source of “empirical data” regarding the correlation and indeed identification of mental and cerebral processes. David Hartley’s theory in his 1749 Observations on Man was, as is well known, republished in abridged form by Priestley, but he discards Hartley’s “vibratory neurophysiology” while retaining the associationist framework, although not because he disagreed with the former. Yet Hartley was, at the very least, strongly agnostic about metaphysical issues (and it is difficult to study these authors while bracketing off religious considerations). One could see Locke and Hartley as articulating programs for the study of the mind which were more or less naturalistic (more strongly so in Hartley’s case) while avoiding “materialism” per se; in contrast, Priestley bit the (materialist) bullet. In this paper I examine Priestley’s appropriation and reconstruction of this “micro-tradition,” while emphasizing its problems.