Abstract In his paper “Idealism and Greek Philosophy: What Berkeley Missed and Descartes Saw,” Myles Burnyeat purports to show not only that idealism was not endorsed by any ancient philosopher, but also that it could not have been endorsed before Descartes; Greek philosophy was dominated by an “unquestioned, unquestioning assumption of realism.” By ‘idealism,’ Burnyeat means mainly Berkeley’s immaterialism, but he also extends his demonstration to something more akin to Kant’s transcendental idealism. After arguing that this last version has more historical credentials to the title of idealism than Berkeley’s doctrine, I compare Burnyeat’s reading to Natorp’s interpretation in Platos Ideenlehre, subtitled “An Introduction to Idealism.” Natorp argues that there is, on the contrary, a kind of underlying idealism in Greek philosophy, one that can be discerned on the basis of an interpretation of the meaning of the verb ‘to be’ which has found support in more recent research.