 This question of whether real essences could be the foundation of natural kinds for Locke is as old as the Essay itself. Both Gottfried Wilhelm Leibniz and Edward Stillingfleet, Lord Bishop of Worcester, point out that Locke’s position on real essences seems to entail that there are natural kinds based on similarities among the real essences. As Leibniz put it in his critique of the Essay entitled New Essays on Human Understanding (1704),