the insistence that improvement can come only through human effort, provides the solution to the puzzle that is otherwise so baffling—the resilience of progressive ideology in the face of discouraging events that have shattered the illusion of utopia. The idea of progress never rested mainly on the promise of an ideal society—not at least in its Anglo-American version. Historians have exaggerated the utopian component in progressive ideology. The modern conception of history is utopian only in its assumption that modern history has no foreseeable conclusion. We take our cue from science, at once the source of our material achievements and the model of cumulative, self-perpetuating inquiry, which guarantees its continuation precisely by its willingness to submit every advance to the risk of supersession.

That nothing is certain except the imminent obsolescence of all our certainties—our scientific theories, our technology, our artistic styles and schools, our philosophies, our political ideals, our fashions—naturally gives rise to the sense of impermanence that has been celebrated or deplored as the very essence of the modern outlook, the sense that "all that is solid melts into air," in the often quoted remark by Marx and Engels. What is less often remarked is that impermanence appears to assure a certain continuity in its own right when conceived as an extension of the self-correcting procedures of scientific discovery, which allow the scientific enterprise as a whole to flourish in spite of the constant revision of particular findings. A social order founded on science, with its unnerving but exhilarating expansion of our intellectual horizons, seems to have achieved a kind of immortality undreamed of by earlier civilizations.

Whatever else we can say about the future, it appears that we can safely take for granted its sophisticated contempt for the rudimentary quality of our present ways. We can imagine that our civilization might blow itself up—and the prospect of its suicide has a certain illicit appeal, since at least it satisfies the starved sense of an ending—but we cannot imagine that it might die a natural death, like the great civilizations of the past. That civilizations pass through a life cycle analogous to the biological rhythm of birth, maturity, old age, and death now strikes us as another discredited superstition, like the immortality of the soul. Only science, we suppose, is immortal; and although the unlikelihood of its melting away can be experienced even more intensely, perhaps, as a curse than as a blessing, the apparently irreversible character of its historical develop

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