 The model that serves the Craftsman is regularly named the “Living Thing (Itself),” and this is either a form, or an appropriately organized constellation of forms. It is the Ideal (or better: Real) Universe; the object of what Plato had called “real astronomy” (as opposed to empirical astronomy) in the Republic (527d–531d, esp. 530a3). The Craftsman does not—indeed logically cannot—copy by replicating the Living Thing; his challenge rather lies in crafting an image of it that is subject to the constraints of becoming: unlike the model, it must be visible and tangible (28b7), hence three-dimensional (solid—stereoeidê, 32b1). This constraint in turn requires the postulation of something three-dimensional in which the created universe may subsist , what Timaeus initially names the “receptacle (hupodochê) of all becoming” (49a5–6) and subsequently calls “space”(chôra, 52a8, d3).