Elisabeth was the first of Descartes' interlocutors to press concerns about mind-body union and interaction, and the only one to receive a detailed reply, unsatisfactory though she found it. Descartes took her tentative proposal `to concede matter and extension to the soul' for a confused version of his own view: `that is nothing but to conceive it united to the body. Contemporary commentators take Elisabeth for a materialist or at least a critic of dualism. I read her instead as a (...) dualist of a different variety from Descartes: a forerunner of twenty-first century naturalistic dualism which calls for empirical investigation of the psychological and its posits to be taken just as seriously as physics and its posits. -/- I argue that Elisabeth, a keen scholar of mechanistic physics, objected not to substance dualism per se but to the residual Scholasticism of Descartes' account of mind-body causality and his dogmatism about principal attributes. She queried Descartes' categorisation of the `action' of thought as mind's principal attribute, and his identification of it with the merely negative property of immateriality, holding instead that further philosophical and empirical investigation into the nature of the mind is necessary. I problematise the materialist interpretation of Elisabeth with reference to later letters where she dismissed the materialist Objections of Hobbes and Gassendi and continued to urge further clarifications to Cartesian dualism. I explore Elisabeth's contrasting of statements of mechanistic physics with statements about thought, and her call for further investigation into the properties of the mind, and argue they mark her out as a forerunner of contemporary naturalistic dualism which proposes substance dualism as a best interpretation of recent psychology and of the difference in logical form between current physics and current psychology. (shrink)