Some scholars believe Plato intended to write a trilogy consisting of Politikos (later period, 365-361 b.c.e.; Statesman, 1804), the Sophist, and a third dialogue on the philosopher. Because the first two dialogues search for definitions that not only will delimit the statesman and the Sophist but also will show how, if at all, they differ from the philosopher, it seems likely that Plato planned a third dialogue in which he would define the philosopher and describe the appropriate search for knowledge. In the Sophist, Plato defines Sophists and describes the kind of activity that properly belongs to them. The dialogue Theaettos (middle period, 388-368 b.c.e.; Theaetetus, 1804) is also intimately connected to this series, for in it Plato begins the quest for a proper definition of knowledge and for an answer to many of the problems that plagued him as he worked out his theory of ideas. The Sophist follows Theaetetus and carries on the search for an answer.