The following summary of the book is based on Nehamas's introduction. Kaufmann seeks to counter the distorted understanding of Nietzsche as a psychologically flawed, totalitarian, irrationalist, and anti-semitic thinker who deserves to be either ignored or denounced. He places the responsibility for the creation of this Nietzsche "legend" partly on Stefan George and his followers, but mainly on Nietzsche's sister, Elisabeth Förster-Nietzsche, who controlled the publication of his works and sometimes even changed his language. Kaufmann shows that The Will to Power, which she edited and published, is an arbitrary selection of Nietzsche's notes, taken out of context and chronological order and arranged according to Förster-Nietzsche's flawed understanding of her brother's thought. Kaufmann argues that Nietzsche acquired his reputation for heartless cruelty, anti-semitism, and pervasive self-contradiction because critics felt free to quote short passages of his work, often written in exaggerated language, without concern for context.
In Kaufmann's view, Nietzsche's style indicates a specific approach to philosophical questions: it expresses the desire to look at things from as many different perspectives as possible and a willingness to "experiment" with ideas. By describing Nietzsche's concerns as "existential", Kaufmann connects him to the existentialism of Søren Kierkegaard, Martin Heidegger, and Jean-Paul Sartre. Kaufmann sees Nietzsche as an heir to rationalism, rather than a Romantic critic of the Enlightenment. Nietzche's ideal type is not Napoleon Bonaparte or Adolf Hitler, but Johann Wolfgang von Goethe, who conquered not the world but himself. Kaufmann concludes that Nietzsche's philosophy has its roots in Immanuel Kant, Georg Wilhelm Friedrich Hegel, and Socrates, who "became little less than an idol for him." He rejects the interpretation of Nietzsche's overman as a biological category referring to a German master race whose will to power would lead it to exploit the rest of the world. While Kaufmman admits that Nietzsche sometimes invites misunderstanding, he insists that overcoming, the chief attribute of the overman, involves the sublimation of people's baser impulses, the cruder forms of the will to power, an effort guided by the will to power itself in the form of rationality. The overman is thereby able to able to face the eternal recurrence, which Kaufmann understands to mean that the universe repeats itself in exactly the same way endlessly and without purpose. Nietzsche, as Kaufmann interprets him, is an enemy of all versions of the state, both totalitarian and liberal: he is an "anti-political" thinker for whom individualism is a greater value than any collective good. Kaufmann considers Nietzsche's judgments balanced and reasonable. While in The Birth of Tragedy (1872), Nietzsche pits Apollo, the form-giving God, against Dionysus, the god of formless frenzy, Apollo gives way to Dionysus, who has become a synthesis of the two, "passion controlled." In On the Genealogy of Morality (1887), Nietzsche explains modern morality as a transformation of an early form of Homeric "master" values into a "slave" morality aimed at safeguarding the interests of the weakest members of society, but does not side with either master or slave morality, aiming to go beyond both.