This study focuses on Plato's "problem" with Sophistry. In recent years, that "problem" has come to be understood either as Plato's disagreement with the "philosophical" doctrines of the ancient Sophists or as his unreflective condemnation of their way of life. Hegel is responsible for the first way of thinking, Nietzsche for the second. For both, the "problem" posed by the ancient Sophists was of considerable importance. It confronted Plato with the challenge that philosophy justify itself--a challenge which Plato could not fully understand and which he failed to meet. According to Hegel, the challenge posed by the Sophists cannot be met by advancing a doctrine. It can only be met dialectically. According to Nietzsche, it cannot be met at all for the Sophist is justified in his rejection of the "rules" of all philosophical discourse, including dialectical argument. After offering some historical background on the ancient Sophists, I examine Hegel's and Nietzsche's understanding of Plato's "problem" with them. My argument is that both are correct to identify the "problem" posed by the Sophists as a challenge that philosophy provide for itself a justification. I argue that Hegel is right to conclude that such a justification can only be given dialectically but that Nietzsche teaches us that it must be conducted in an ad hominem manner. Contrary to both, I argue that Plato understood this very well and that the dialogues are written in accordance with this understanding. I then focus on the drama of the Sophist in order to show that Plato fully understood the challenge posed by the ancient Sophists and that his response to it is adequate. Plato does not think that the challenge of the Sophist can be met for once and for good. For that reason, the philosophical life is justified. / Thesis / Doctor of Philosophy (PhD)