Plato famously promised to complement the Sophist and the Statesman with another work on a third sort of expert, the philosopher--but we do not have this final dialogue. Mary Louise Gill argues that Plato promised the Philosopher, but did not write it, in order to stimulate his audience and encourage his readers to work out, for themselves, the portrait it would have contained. The Sophist and Statesman are themselves members of a larger series starting with the Theaetetus, Plato's investigation of knowledge, and the whole series relies on the Parmenides, the second part of which presents a philosophical exercise, introduced as the first step in a larger philosophical program. Gill contends that the dialogues leading up to the missing Philosopher, thoughthey reach some substantive conclusions, are philosophical exercises of various sorts designed to train students in dialectic, the philosopher's method; and that a second version of the Parmenides exercise, closely patterned on it, spans parts of the Theaetetus and Sophist and brings the philosopher into view. This is the exercise about being, the subject-matter studied by Plato's philosopher. Plato hides the pieces of the puzzle and its solution in plain sight, forcing his students (and modern readers) to dig out the pieces and reconstruct the project. Gill reveals how, in finding the philosopher through the exercise, the student becomes a philosopher by mastering his methods. She shows that the target of Plato's exercise is internally related to its pedagogical purpose.