THE POLITICAL MYTHOLOGY OF APARTHEID. By Leonard Thompson. Yale University Press. 293 pp. $22.50.

MYTH IS the mother of ideology. In primitive society it expresses and justifies the collective wisdom of the tribe as well as its material and moral circumstances. Above all, it reveals or lends significance to a way of life. But modern societies also require myths. They are useful to bolster or break a regime, especially a regime already threatened from without and/or within.

These are some of the considerations explored by Leonard Thompson in The Political Mythology of Apartheid. He suggests replies to questions as basic as: "Can a regime expect to endure without a credible political mythology? Or, when a regime is under extreme stress, can it transform its mythology into one that legitimates a policy of survival, regardless of intellectual and moral defects?"

In 1980 Marianne Cornevin published, for UNESCO, a study called Apartheid: Power and Historical Falsification in which she examined 10 South African historical myths, most of them having to do with black/white relations, such as the beliefs: that whites and blacks arrived in the country at the same time; that blacks had been migrants until they met whites; that Boer migrants in the interior advanced into an unpopulated land that belonged to no one, etc. According to Thompson, these myths are incorporated into the larger one of "unassimilable races," which holds that black society is fragmented into discrete "tribal" groups, while white society constitutes a single organic unit, as opposed to white hegemony.

Little in Thompson's book is particularly new. In addition to Cornevin's study, he also draws heavily on Richard Elphick's pioneering examination of Khoisan history in Kraal and Castle, and on the invaluable documentation provided by Elphick and Hermann Giliomee in The Shaping of South African Society 1652-1820, and by Andr,e du Toit and Hermann Giliomee in Afrikaner Political Thought: Analysis and Documents, 1780-1850.

This means that much in Thompson's book is not particularly new. But it is in his overall portrayal of the emergence, adaptation and manipulation of core myths in the shaping of the apartheid ideology that he offers a study both illuminating and fascinating, both scholarly and immensely exciting. In fact, The Political Mythology of Apartheid may well be termed required reading for anybody wishing to comment on the convulsive tragedy being enacted by South Africa at this moment.

Thompson places South African mythology within the context of "political mythology in the modern world." And he explains persuasively the emergence of Afrikaner nationalist mythology, mainly under pressure from two sources: the first exerted by British imperialism, the second by indigenous peoples -- the first leading to a struggle for Afrikaner liberation, the second to the suppression of blacks.

IT IS A PITY that Thompson's picture of early white South African society prior to the advent of the British is sometimes too scant to do justice to the peculiar nature of black/white relations before the 19th century, although he does mention that "during the seventeenth century the Europeans at the Cape had no sense of innate racial superiority over the indigenous peoples but they felt justified in subduing them because they were not Christians." He also ignores the contribution of Scottish missionaries to the rise of the curious brand of Calvinism associated with the the Afrikaner.

However, Thompson does provide a lucid account of how those pernicious myths still used to justify apartheid developed, how they were manipulated and perpetuated through the churches, through the rise of the secret society known as the Broederbond, through the use of special history textbooks in schools, and through literature. (It is a pity, in this last respect, that Thompson fails to refer to a number of early Afrikaans writers, from Eugene Marais onwards, who specifically attacked those crystallizing myths.)

Thompson examines in depth three individual myths or clusters of myths: those of the "unassimilable races"; the so-called myth of Slagtersnek, in which a group of Boers, who had led a half-hearted uprising in the eastern frontier in 1815, were hanged by British officials near the town of Slagtersnek and then subsequently resurrected as heroes and martyrs by later generations; and the Covenant, the vow made by the "Voortrekkers" or Boer emigrants in 1838, before the battle of Blood River against the Zulus, to celebrate victory by building a church and by commemorating the event as a sacred day.

Thompson perceptively, even brilliantly, analyzes the historical inaccuracies of these myths. He shows how gradually myths surrounding the race issue came to dominate the contemporary scene, how a group of outcasts, admired only by their immediate kin, were transformed into heroes by later generations when a myth, i.e. Slagtersnek, was required to break British domination, and how a Covenant, forgotten, it seems, by the very people who made it, was subsequently resurrected when Afrikaner survival (or chauvinism?) required a myth.

The most illuminating chapter in the book is called "Adaptation and Erosion of the Afrikaner Nationalist Mythology." In it, Thompson demonstrates quite startlingly the adaptability of myths: whereas Slagtersnek has practically faded out of political existence, the Covenant has entered into a period of moral crisis, while the cluster of myths supporting the unassimilability of races (i.e. the "disparate and incompatible ethnic and racial groups") in South Africa still rules supreme. It has been subjected to its most severe ordeals ever, both from the world outside and from within. Whereas for so many years these myths "provided legitimacy for the regime," both mythology and regime seem to be reeling at the moment.

For an understanding of why apartheid has survived for so long, and for an appreciation of the critical phase it has entered, Leonard Thompson's study is absolutely essential. Many of the disgusting oversimplifications and distortions propagated by, among others, James Michener in The Covenant, are at last unmasked and destroyed; and in providing a "historical dimension to the role of ideas" Thompson has provided insights so often lacking in the more facile generalizations about "the South African situation".