 Thus here, in the Prolegomena, Kant describes what he calls Hume’s “challenge” to reason concerning “the connection of cause and effect” in precisely the same terms that he had himself earlier used, in the 1763 essay on Negative Magnitudes and the 1766 Dreams of a Spirit-Seer, to pose a fundamental problem about the relation of a real ground (as opposed to a logical ground) to its consequent.