IN THE Winter 1999/2000 issue of The National Interest, Alan Charles Kors asked, "Did Western civilization survive the twentieth century?" He concludes, rather optimistically, that despite its many critics Western civilization has emerged resilient, as it had from so many previous, darker times. But Kors, engaged in a lengthy jeremiad against the multiculturalist Left, misses a critical feature of the past century: a far deeper, more pervasive attack from which the West has not yet recovered.

The twentieth century will ultimately be remembered for its challenges to certainty. All of the major themes historians have pointed to as markers of our age can be subsumed within this paradigm. More than any previous period, the twentieth century called into question many of the fundamental beliefs upon which Western civilization had been based. Notions of class privilege, racial hierarchies, gender roles and sexual identities all underwent dramatic rethinking and led to readjustments in political, social and economic relations. Beyond grand societal transformations, certainties upon which individuals had always counted--such as where to live, what occupation to enter, whom to marry, and even what would become of one after death--ceased to be sure. As political and social traditions were being questioned, so too were basic assumptions in the sciences and philosophy. The multiculturalists' assaults upon Western civilization, which Kors adroitly parries, scarcely equaled the mighty blows struck by those from within the very heart of the Western scientific tradition.

THE TWENTIETH century began with Einstein's sweeping away of several fundamental human, not simply scientific, assumptions. Einstein's theories gained worldwide attention for suggesting that two dimensions always assumed to be constants--time and space--were in fact curved and relative, dependent on that which interacts with them. Newtonian mechanics, the basis of Enlightenment advances, no longer functioned in the expanding universes of astrophysics and subatomic particles. If the very dimensions in which we exist were not absolute, what absolutes could we hold on to?

At least there was the certainty that one and one makes two. Or rather there had been, until Kurt Gödel came along. Gödel saw that mathematics was based upon assumptions, not indisputable truths. His infamous incompleteness theorem, published in 1931, argued that the system upon which mathematics is partly based is unprovable because in a logical system using symbols to construct axioms, any proof must come from outside that system. One plus one, therefore, equals two only because there is consensus that it is so. Just how far could relativity be taken?

Werner Heisenberg's uncertainty principle reached into the subatomic realm. Stating that we can never know both the position and the speed of any particle, Heisenberg's theories have influenced contemporary notions of probabilistic occurrences, in which we are now only able to speak of a particle's probability of existing in any given space or time. Praising Western civilization's resilience, Kors writes: "Greece fell, but its mathematics still measures, actually and metaphorically, the world." Its mathematics does still measure the world, but the twentieth century saw Western sciences ability to measure with certainty undermined from within its finest ranks.

The notion that nature behaved with regularity and that humans could measure and predict its patterns with precision formed a salient aspect of Enlightenment thinking, but this notion crumbled in our age of uncertainty. Chaos theory, first formulated by the French mathematician Henri Poincaré in the latter half of the nineteenth century, but developed and tested in the 1960s by the American meteorologist Edward Lorenz, maintains that long-range prediction is impossible. Systems sensitive to their initial conditions can exhibit chaotic behavior where tiny errors at the start become gigantic ones later. Chaos theory, which extends to countless other systems, from weather patterns to water flow to leaky faucets, exposed the inability of science to predict with certainty.

When James Watson and Francis Crick unlocked the structure of DNA, genetic programming became virtually inevitable. Soon we would know the sex of an unborn child. By the century's final decade, human ears were being grown on the backs of mice, Dolly the sheep made cloning a living, tangible reality, and scientists spoke of the ability to create life. In 1999 the human genome project unraveled the first pair of human chromosomes and promises shortly to map the entire digital code that determines much of human identity. This undertaking represents far more than just an extraordinary advance in knowledge. If we discover that our genetic programming determines most of our personality, emotional make-up and spiritual inclinations, it may well present a challenge to the millennia-held notion of a soul.

PHILOSOPHY followed suit with science in the century's long march toward uncertainty. Jean-Paul Sartre and Albert Camus popularized in existentialism the view that the world was a chaotic place, not divinely ordered, and this notion has enjoyed worldwide popularity. While Nietzsche's proclamation that God is dead represented an extreme, the open questioning of God's existence was a leitmotif of the twentieth century.

Not only did the truth of God's existence and his ordered universe fall prey to attack, but the very notion of truth itself fell into doubt as Michel Foucault argued, among other things, that the basic assumptions that societies take for granted as truths are wholly dependent upon power relations and are therefore fluid over time. Foucault's relativism struck at the heart of commonly accepted Western beliefs and challenged the idea that anything could be established with certainty.

Perhaps the most common feature attributed to the twentieth century is that it witnessed the greatest violence in human history. Yet the great tragedy of the century's carnage was nor solely that it wrought death and suffering of a magnitude hitherto unknown, but that it challenged citizens' faith in the modern state. After Stalin's purges and Nazi terror it became clear that the full power of the modern state could be harnessed not only for civilizing and improving social conditions, but also for the destruction of whole peoples.

Even if the state were unlikely to inflict terror upon its own citizens, its ability to protect them against foreign attack seemed questionable. A profound change occurred in the way people conceptualize war. With the advent of thermonuclear weapons and delivery systems capable of projecting warheads around the globe, the nuclear age redefined the potential devastation of war, holding forth the prospect of the planer's total destruction. Post-Cold War triumphalism casts a dense fog upon our memories of bomb shelters and missile attack drills, but the uncertainty that surrounded a nuclear holocaust was once, and not so long ago, as palpable as today's jubilation over stock market booms.

In addition to scientific development and unparalleled violence, one other salient trend of the last century often cited is the magnitude and rapidity of social change. Groups traditionally marginalized by elites broke through rigid class, race and gender barriers to attain varying degrees of control over their own destinies. These social upheavals, too, can be seen as challenges to certainty, for they questioned the long-existing order on which societies were based.

As class certainties gave way to greater social mobility, so too did notions of racial supremacy. Even the one great certainty on which all men could rely--that a woman's place is in the home--crumbled in the last century. The growing acceptability of "coming out", the open assertion that women did not need men in their lives for sexual gratification, and the increasing openness of bisexuality--a behavior proclaiming that sexual identities are fluid--have all produced a kind of sexual glasnost, whereby a once taboo topic not only penetrated mass media, but threatened the most basic societal norms.

PROFESSOR Kors' question is a good one, and the answer is surely yes. The more interesting question is: What damage did the twentieth century inflict? The principal themes of that century--scientific advances, social change and barbarity--can all be seen as challenges to certainty, and it is this idea for which the past century will eventually be remembered. That the West will recover all or even most of its lost assumptions is unlikely. The West may, however, invest in new canons. Faith in the state may already be in the process of being supplanted by faith in markets. Faith in God may rise among some as an ultimate reaction to uncertainty. But will there again be faith in absolutes?

Lurking just below the surface of these reflections is yet another question: whether there is some link between the century's great themes--between unprecedented horrors, genocides and brutality on the one hand and the scientific, philosophical and social challenges to certainty on the other. Did Heisenberg and Foucault merely reflect the growing uncertainty of the century, or could its catastrophic man-made upheavals have been caused by the unmooring of previously unshakable beliefs? This is a question whose answer is as uncertain as the age itself.

Zach Shore is a national security fellow at the John M. Olin Institute for Strategic Studies, Harvard University.