That a psychologist without equal speaks from my writings, is perhaps the first insight reached by a good reader - a reader as I deserve him, who reads me the way good old philologists read their Horace. (Nietzsche, Ecce Homo)
Nietzsche repeatedly insisted on his importance first and foremost as a psychologist, but this has not always been taken as seriously as it ought to be, especially by philosophers. Philosophers tend to insist on the truth of a belief, but psychologists are more interested in why one believes what one believes. “The falseness of a judgment is not for us necessarily an objection . . . The question is to what extent it is life-preserving.” Philosophical doctrines also carry with them a strong sense of universality and necessity, while psychological analyses remain inevitably bound to the particular contingencies of a personality or a people. But Nietzsche was suspicious of claims to universality and necessity, and he almost always preferred the witty, dazzling or even offensive psychological insight to a grand philosophical thesis. Writing about Socrates, he began, “In origin, Socrates belonged to the lowest class: Socrates was plebs. . . . he was ugly.” On Kant, he noted, “The instinct which errs without fail, anti-nature as instinct, German decadence as philosophy - that is Kant!” On the “shabby” origins of morality as such he suggested, “The slave revolt in morality begins, when ressentiment itself becomes creative and gives birth to values.” And on German philosophy, he complains, “How much beer there is in the German intelligence!” He saw himself and praised himself as a diagnostician, and his philosophy consists to a very large extent of speculative diagnoses, concerning the virtues and vices of those whom he read and read about, whose influence determined the temper of the times. His central strategy, accordingly, was the use of the ad hominem argument, a rhetorical technique often dismissed as a “fallacy,” an attack on the motives and emotions of his antagonists rather than a refutation of their ideas as such. (“We know, we can still see for ourselves, how ugly [Socrates] was. But ugliness, in itself an objection, is among the Greeks almost a refutation.”)