THERE IS A KIND OF MADNESS, said Plato in the Phaedrus, which confers the gift of prophecy and which is "the source of the greatest blessings" among men. Twenty-two hundred years later, the German philosopher Friedrich Nietzsche not only echoed Plato's claim by noting that the mad have traditionally been regarded as the "mouthpieces" of truth, but tried to fashion his own life and work for just such a role.

Many would agree today that he was highly successful. Although Nietzsche was not declared clinically insane (the cause is thought to have been syphilis) until the age of 44, 11 years before his death in 1900, most of the works for which he is famous today, from Thus Spoke Zarathustra to Ecce Homo, were written in a state of mind that was lucid but not expecially sane. Moreover, out of the mouth of this foremost of modern madmen came "truths" to which the world of the 20th century has listened in rapt attention. Today, Nietzsche, whose writings were almost completely unknown until after his final collapse, is widely regarded not only as among the outstanding philosophers of all time but as one of the masters of the German language.

Yet, for all that, Nietzsche's prophecies have been treated like curses as much as blessings. Due partly to his sister Elisabeth's falsification of his manuscripts, after his breakdown, to conform to her own proto-Nazi beliefs, and partly to his association, while still a young professor of classical philology, with the composer (and anti-Semite) Richard Wagner, Nietzsche's philosophy was for a long time interpreted as being fascistic and anti-Semitic. Nazi Alfred Rosenberg even went so far as to call Nietzsche "the father of National Socialism." Today, however, most scholars give such characterizations little credence, noting that Nietzsche unequivocally denounced anti-Semitism and German nationalism in his writings. It has been pointed out, for example, that Thus Spoke Zarathustra, which the Nazis "honored" by placing in the Tannenberg Memorial together with Hitler's Mein Kampf, condemns the fascist state as "a cold monster." As for Wagner, Nietzsche eventually wrote a book and a pamphlet harshly criticizing him, the latter titled Nietzsche Contra Wagner.

Nonetheless, there remains today a sentiment of mistrust and misgiving toward Nietzsche which no number of antifascist quotes is likely to allay. This sentiment is due not only to the radical nature of Nietzsche's views -- particularly his moral ones -- but to the highly dramatic form in which he expressed them. The philosopher of the will to power desired that his ideas be thought of as "dangerous" and certainly in this respect at least his wishes have been granted. The modern world has listened to Nietzsche much as the ancient world listened to the detached voices of the deranged, partly in fear and revulsion for what seemed to be the destructive consequences of his "truths," and partly in a kind of ecstasy of curiosity to know and experience them as he did. Just what Nietzsche did experience -- and what in him the modern world seems simultaneously to revile and revere -- is the theme of this splendid biography by Ronald Hayman. Combining remarkable philosophical sophistication with solid scholarship and a detached but effective narrative style, Hayman sounds for us the shrill blessing with which Nietzsche, through the oracle of his life and work, sought to shatter the ears of the modern world.

The principal theme of Hayman's biography is Nietzsche's tendency "to take sides against himself" in all he did and thought -- to value any experience, even illness, for its ability to militate against his own self-satisfaction and complacency. This tendency is prominent in many of the major decisions he made during his lifetime, from his resolution as a young man to give up his plans to become a clergyman, to his repudiation of Wagner at a high point of the composer's fame, to his abandonment of a brilliant academic career at the age of 34. The manner in which Nietzsche regarded these decisions is brought out in the following statement quoted by Hayman: "I want to make things as hard for myself as they have ever been for anybody; only under this pressure do I have a clear enough conscience to possess something few men have ever had -- wings, so to speak."

But this dimension of Nietzsche's personality can also be seen as an aspect of his philosophy. As Hayman says, the exacting demands Nietzsche placed on himself "led (or at least contributed)" to his views on the nature of mind and self. These views have often been likened to Freud's in their emphasis on the irrational sources of human behavior, but the differences between the perspectives of the two thinkers are just as profound. The nature of these differences can be expressed by saying that while Freud was a depth psychologist, Nietzsche was a psychologist of heights. As the latter put it, "your true nature does not lie within you, deeply concealed, but immeasurably high above you." For Nietzsche, man was the undetermined, perhaps indeterminate animal and the human personality was a "test" which could be known by being continously written, not be being analytically "read out."

Nietzsche's capacity "to take sides against himself," however, can be viewed as a feature of his philosophy in another way. Thus, his well-known attack on Christian morality was at least partly an attack on very strong religious elements within himself; it is only by viewing the philosopher as a "moralist" or as "deeply religious by temperament," in Hayman's words, that this attack can be understood. As Nietzsche said in Zarathustra: "Some god in you converted you to godlessness. Is it not your piety that no longer lets you believe in a god?"

Such passages show not only how far Nietzsche was from embracing the pious atheism of some of his 20th-century followers, but the extraordinary extent to which he forced himself, even in his moral concerns, to live "within the arena of the bull," inside the perimeter of the greatest possible dangers and difficulties to himself. Such an effort, sustained over many years in almost complete solitude, could have only resulted eventually in his being gored and trampled. His final defeat, nonetheless, does not negate the many victories he won. "He was," in the closing words of Hayman's book, "one of the great liberators."