The Conversation that Descartes had with Burman on April 16, 1648 sheds light on the meaning of the phrase ens reale, which was common in modern scholastic treatises but unusual under his pen, and thus on the Cartesian concept of realitas. Ens verum et reale, such is the object of mathematics: no less real than that of physics, even if it does not exist out of the mind and requires imagination. As for the object of metaphysics, if it is no (...) less real than that of physics and mathematics, it is both existent and unimaginable. The answers given by Descartes that are examined here are significant samples which in addition show the need to re-edit the Conversation in the light of Clauberg's Opera. (shrink)