Reading and influenceA trained philologist, Nietzsche had a thorough knowledge of Greek philosophy. He read Kant, Plato, Mill, Schopenhauer and Spir, who became his main opponents in his philosophy, and later Spinoza, whom he saw as his "precursor" in many respects but as a personification of the "ascetic ideal" in others. However, Nietzsche referred to Kant as a "moral fanatic", Plato as "boring", Mill as a "blockhead", and of Spinoza he said: "How much of personal timidity and vulnerability does this masquerade of a sickly recluse betray?".
Nietzsche's philosophy, while innovative and revolutionary, was indebted to many predecessors. While at Basel, Nietzsche offered lecture courses on pre-Platonic philosophers for several years, and the text of this lecture series has been characterized as a "lost link" in the development of his thought. "In it concepts such as the will to power, the eternal return of the same, the overman, gay science, self-overcoming and so on receive rough, unnamed formulations and are linked to specific pre-Platonics, especially Heraclitus, who emerges as a pre-Platonic Nietzsche."
In his Egotism in German Philosophy, Santayana claimed that Nietzsche's whole philosophy was a reaction to Schopenhauer. Santayana wrote that Nietzsche's work was "an emendation of that of Schopenhauer. The will to live would become the will to dominate; pessimism founded on reflection would become optimism founded on courage; the suspense of the will in contemplation would yield to a more biological account of intelligence and taste; finally in the place of pity and asceticism (Schopenhauer's two principles of morals) Nietzsche would set up the duty of asserting the will at all costs and being cruelly but beautifully strong. These points of difference from Schopenhauer cover the whole philosophy of Nietzsche."
Nietzsche expressed admiration for 17th-century French moralists such as La Rochefoucauld, La Bruyère and Vauvenargues, as well as for Stendhal. Harold Bloom has often claimed that the essays of Ralph Waldo Emerson had a profound and favourable influence on Nietzsche. While Nietzsche never mentions Max Stirner, the similarities in their ideas have prompted a minority of interpreters to suggest a relationship between the two. In 1861 Nietzsche wrote an enthusiastic essay on his "favorite poet", Friedrich Hölderlin, mostly forgotten at that time. He also expressed deep appreciation for Stifter's Indian Summer,Meyer-Sickendiek, Burkhard, "Nietzsche's Aesthetic Solution to the Problem of Epigonism in the Nineteenth Century", ed. Paul Bishop, Nietzsche and Antiquity: His Reaction and Response to the Classical Tradition, Woodbridge, UK: Boydell & Brewer, 2004. p. 323 Byron's Manfred and Twain's Tom Sawyer.