Elisabeth of Bohemia's Correspondence with Descartes

Princess Elisabeth of Bohemia (1618–1680), eldest daughter of the deposed "Winter King" Frederick V and granddaughter of James I of England, opened a correspondence with René Descartes in May 1643 that would run for roughly seven years and survive today in 58 letters, 32 from Descartes and 26 from Elisabeth, first published in full only in 1879 by Alexandre Foucher de Careil. Living in exile at The Hague after the Bohemian court's defeat at the Battle of White Mountain in 1620, Elisabeth had been introduced to Descartes's philosophy by a mutual acquaintance, and she opened the exchange with a question that went straight to the unresolved heart of his system: if the soul is an unextended thinking substance entirely distinct from the extended body, as the recently published Meditations on First Philosophy (1641) argued, how can it possibly move the body at all, given that on Descartes's own account causal interaction requires some form of contact or extension? Descartes had proposed the pineal gland as the physical seat of interaction in his earlier, unpublished Treatise on Man, but Elisabeth pressed him to explain the mechanism itself, not merely name a location, and no answer he offered — appeals to "determination" of already-existing motion, then to a supposedly primitive, unanalyzable notion of the union — ever fully satisfied the objection.