HOW do you write a biography of an explorer of whom little is known except that he was the first European to round the Cape of Good Hope and reach India (1497-98) and that in two subsequent expeditions he acted as a Portuguese Cortes, an implacable exponent of main force, invariably described by his chroniclers as angry or indignant?

Sanjay Subrahmanyam solves this problem brilliantly by a sociological approach, whereby Vasco da Gama the man is dissolved into the totality of his multiple impacts on Portugal and the Indian Ocean. Where most biographers aim at empathy and are analogous to Marlon Brando and the Method, Subrahmanyam recalls the Olivier approach to acting, from the outside in. It is a tribute to his exhaustive and inspired scholarship that he carries off his project so successfully.

The author examines the Indian Ocean as Islamic "lake" and the impact of da Gama and the Portuguese on this. His approach is always nuanced. Take the question of whether da Gama introduced a new kind of seaborne violence into the Ocean. Is this true or false? Subrahmanyam says the proposition is false in the sense that piracy and corsair engagements predated the coming of the Europeans.

But it is true in the sense that the Portuguese were the first to use violence systematically and from the vantage point of superior military technology. And the motive for Portuguese expansion into Asia has been much misunderstood. Of course commonsense commercial desire to find an alternative spice route played some part, but more important was King Manuel of Portugal's wish to link up with Prester John, and so catch the Islamic world between two fires.

The legendary Christian king Prester John, originally confused with Genghiz Khan and his successors Ogodei and Kuyuk, who devastated the world of Islam in the thirteenth century, was now supposed to have relocated to east Africa and it was to find him that Portuguese monarchs dispatched Diaz (first man to double the Cape in 1486) and later da Gama.

Portuguese eastward expansion was spurred by the Reconquista and the expulsion of the Moors in Spain, events almost exactly contemporary with the first voyages into the Indian Ocean. Expansion was thus reactive rather than proactive.

The search for Prester John was a search for a Christian ally in a new crusade and was thus in a sense to the Islamic invasion of the Iberian peninsula what the Counter Reformation was to the Reformation. In terms of the history of exploration, one might say that the true synchronicity in the 1490s was the westward voyaging of Columbus and Cabot. To call da Gama a Portuguese Columbus is, therefore, sloppy and inaccurate.

As for the impact of da Gama on Portugal, this was principally to increase royal power enormously. Before da Gama's voyage King Manuel's scope for action had been limited by a jealous nobility and the two powerful military orders, of Christ and Santiago.

Flushed with the success of a new colony in India and enriched by the spoils of the East, Manuel was able to remove these fetters on his royal prerogative. Having won through with da Gama's help, he then rounded on the explorer hero, partly through jealousy, partly because he was incensed at the insubordination in India of the freebooting members of da Gama's extended family. The result was 20 years in the political wilderness for da Gama; he was not recalled as viceroy in India until the accession of a new king.

It is difficult in a short review to do justice to the excellence of this book, which proves conclusively that in the hands of a "greenfingered" historian exhaustive archival research will always pay off. Lest that make the author sound like a mere archive trawler, one should add that this is a book of immense intellectual sophistication.

Some historians claim that biography is an illusion and that in "real" history only the sociological approach works. Subrahmanyam makes this futile "contradiction" between individual psychology and historical structure irrelevant by moving freely between man and context, the empirical and the ii priori, and between history and legend. This is an outstanding book on an important subject. {CORRECTION} 97060200068