Lunacy, Love and Logic : BERTRAND RUSSELL: The Spirit of Solitude 1872-1921.<i> By Ray Monk (The Free Press: $35, 695 pp.)</i>

Ray Monk earned his reputation with an illuminating and hugely readable life of Ludwig Wittgenstein, Bertrand Russell’s celebrated Austrian pupil. A trained philosopher, Monk, who can pursue his quarry with relish, imagination and intelligence, is the perfect biographer for Russell, a brilliant, complex and troubled man whose notoriety has often overshadowed his academic achievements.

A definitive life of Russell has to show his flaws as well as his virtues. Monk does not shirk the task. Russell, a pipe-smoking aristocrat who went to prison for his anti-war views in 1916 and who continued courageously proclaiming them until his death in 1970, provided the framework for the analytical approach that has dominated modern philosophy. Our computer languages had their birth in Russell’s most ambitious project, “Principia Mathematica,” a book so vast that it had to be transported to the publisher in a carriage.

A vigorous campaigner for free trade and women’s suffrage whose social writings helped to reshape attitudes about sex, marriage and education, Russell produced more than 3,000 publications and won the Nobel Prize as well as Britain’s most prestigious honor, the Order of Merit. In his personal life, however, Lord Russell was a man of ruthless egotism, a womanizer capable of uncommon callousness and a father in later life whose behavior led to devastation and tragedy for his descendants (his oldest son went mad; his granddaughter committed suicide). Genius is an insufficient excuse. But Monk’s achievement is to provide a convincing history and explanation for the duality of his extraordinary subject’s character.

The key, in Monk’s view, lies in Russell’s background and upbringing. His father’s family, who traced their lineage back to the time of the Norman Conquest, had a proud history of fighting for their beliefs; Russell was brought up to believe that opposition is a healthy and necessary political activity.

Russell’s sister and both of his parents were dead by the time he was 4; he and his older brother, Frank, were moved into the sternly religious care of their grandmother, Lady Russell. Frank rebelled and was sent away to school. Bertrand, a shy and obedient child, was tutored at home and subjected to his grandmother’s fierce views of duty and obligation. Terrified to admit that he did not share his grandmother’s faith in the Almighty, young Bertie hid his religious doubts in cipher disguised as a Greek exercise book.

Russell’s “Autobiography” offers a memorable account of his unhappy upbringing. Monk has probed more deeply to suggest that his growing awareness of a family history of insanity had as profound an effect on Russell’s character as did his grandmother’s rigid puritanism. Russell admitted to dreaming that his mother had been secretly confined to an asylum and later described his grandmother’s home as “a family vault haunted by maniacs.” His eager interest in Henrik Ibsen’s darkest plays and a readiness to identify himself with Rogojin, Feodor Dostoevsky’s sinister and embittered murderer, are used by Monk to argue a persuasive case for the strength of this obsession with madness. It was, he suggests, fear of insanity that caused Russell to react to the power of his own emotions with such intense alarm and apprehension. Fierce mental activity was, for many years, his chosen weapon against hysteria.

Russell was 20 when he fell in love with Alys Pearsall Smith, a pretty, high-minded and independent American Quaker. Smith’s age--she was five years older than Russell--her unconventional family and rumors that she, too, came from a mentally unstable brood were sufficient reasons for Russell’s grandmother to oppose such a marriage with ruthless determination. The story of Russell’s first marriage does not do him much credit. A flirtation with Smith’s more sensual sister was followed by further dalliances.

The fact that this was a period of intense mental activity and the writing of some of Russell’s most important work cannot obscure the awfulness of his behavior toward his wife. She was reduced to the level of a sexless domestic drudge, and her tears were met with complaints that she was wasting his valuable energy. When, in 1911, Russell began a relationship with Lady Ottoline Morrell that marked his shift from mathematics to philosophy, Smith was told to protect her husband’s career--and Morrell’s marriage--by keeping the affair secret. She tried to do so. She remained in love with Russell for the rest of her life.

Russell’s long and passionate affair with Morrell, a deeply religious woman who refused to leave her husband or to give her lover the child he craved, is rightly connected by Monk to Russell’s quasi-religious yearning for a transcendent belief that his rigorous mind was unable to justify. His letters to her, amply quoted here, show the three passions that he described as governing his life: “the longing for love, the search for knowledge, and unbearable pity for the condition of mankind.” Morrell, if she sometimes swept Russell to the verge of despair and thoughts of suicide, also lifted him to the ecstatic heights in which he produced some of his finest work. Monk, too, seems to have fallen under her spell; the affair with Morrell sometimes threatens to overshadow Russell’s philosophic achievements.

Morrell’s sexual reluctance resulted in some memorably bizarre entanglements for Russell during her reign; one of them was engineered by Morrell herself. She was not, however, responsible for Russell’s affair with Vivien Eliot, wife of the poet, who was for a short period Russell’s pupil. Monk is the first to reveal that the relationship was far more than a one-night stand and that it probably contributed to Vivien Eliot’s mental breakdown.

Morrell’s successor, a spirited and beautiful young actress, Colette Mallinson, wrote herself out of his future by refusing to relinquish her career for motherhood. By the time Mallinson had decided that a mother’s role was not, after all, impossible, Russell was already expecting a child with Dora Black, a left-wing feminist. Russell promptly divorced Smith in order to legitimize his son’s rights to the family earldom.

Promiscuous and callous though Russell is shown to have been, Monk seldom loses sight of his subject’s essential nobility, of the energy and passion with which he pursued knowledge and with which he, along with geniuses of the ilk of Aristotle, Einstein and Newton, helped transform our view of the world. “Isn’t it hard to put him quite out of one’s mind?” Vivien Eliot wrote to Morrell after her own unhappy affair with him. Readers of this magnificent book can share Eliot’s fascination while being spared the pain.