IN contrast to widespread opinion, I believe that the Enlightenment thinkers of the seventeenth and eighteenth centuries got it mostly right. The assumptions they made about a lawful material world, the intrinsic unity of knowledge, and the potential for indefinite human progress are the ones we still take most readily to heart, suffer without, and find maximally rewarding as we learn more and more about the circumstances of our lives. The greatest enterprise of the mind always has been and always will be the attempt to link the sciences and the humanities. The ongoing fragmentation of knowledge and the resulting chaos in philosophy are not reflections of the real world but artifacts of scholarship.
The key to unification is consilience. I prefer this word to "coherence," because its rarity has preserved its precision, whereas "coherence" has several possible meanings. William Whewell, in his 1840 synthesis The Philosophy of the Inductive Sciences, was the first to speak of consilience -- literally a "jumping together" of knowledge as a result of the linking of facts and fact-based theory across disciplines to create a common groundwork of explanation. He wrote, "The Consilience of Inductions takes place when an Induction, obtained from one class of facts, coincides with an Induction, obtained from another different class. This Consilience is a test of the truth of the Theory in which it occurs."
Consilience can be established or refuted only by methods developed in the natural sciences -- in an effort, I hasten to add, not led by scientists, or frozen in mathematical abstraction, but consistent with the habits of thought that have worked so well in exploring the material universe.
The belief in the possibility of consilience beyond science and across the great branches of learning is a metaphysical world view, and a minority one at that, shared by only a few scientists and philosophers. Consilience cannot be proved with logic from first principles or grounded in any definitive set of empirical tests, at least not any yet conceived. Its best support is no more than an extrapolation from the consistent past success of the natural sciences. Its surest test will be its effectiveness in the social sciences and the humanities. The strongest appeal of consilience is in the prospect of intellectual adventure and, if even only modest success is achieved, a better understanding of the human condition.
To illustrate the claim just made, think of two intersecting perpendicular lines, and picture the quadrants thus created. Label one quadrant "environmental policy," one "ethics," one "biology," and one "social science."
We already think of these four domains as closely connected, so rational inquiry in one informs reasoning in the other three. Yet each undeniably stands apart in the contemporary academic mind. Each has its own practitioners, language, modes of analysis, and standards of validation. The result is confusion -- and confusion was correctly identified by Francis Bacon, four centuries ago, as the direst of errors, which "occurs wherever argument or inference passes from one world of experience to another."
Next imagine a series of concentric circles around the point of intersection.
As we cross the circles inward toward the point at which the quadrants meet, we find ourselves in an increasingly unstable and disorienting region. The ring closest to the intersection, where most real-world problems exist, is the one in which fundamental analysis is most needed. Yet virtually no maps exist; few concepts and words serve to guide us. Only in imagination can we travel clockwise from the recognition of environmental problems and the need for soundly based policy to the selection of solutions based on moral reasoning to the biological foundations of that reasoning to a grasp of social institutions as the products of biology, environment, and history -- and thence back to environmental policy.
Consider this example. Governments everywhere are at a loss regarding the best policy for regulating the dwindling forest reserves of the world. Few ethical guidelines have been established from which agreement might be reached, and those are based on an insufficient knowledge of ecology. Even if adequate scientific knowledge were available, we would have little basis for the long-term valuation of forests. The economics of sustainable yield is still a primitive art, and the psychological benefits of natural ecosystems are almost wholly unexplored.
The time has come to achieve the tour of such domains in reality. This is not an idle exercise for the delectation of intellectuals. The ease with which the educated public, not just intellectuals and political leaders, can think around these and similar circuits, starting at any point and moving in any direction, will determine how wisely public policy is chosen.
To ask if consilience can be gained in the domains of the innermost circles, such that sound judgment will flow easily from one discipline to another, is equivalent to asking whether, in the gathering of disciplines, specialists can ever reach agreement on a common body of abstract principles and evidential proof. I think they can. Trust in consilience is the foundation of the natural sciences. For the material world, at least, the momentum is overwhelmingly toward conceptual unity. Disciplinary boundaries within the natural sciences are disappearing, in favor of shifting hybrid disciplines in which consilience is implicit. They reach across many levels of complexity, from chemical physics and physical chemistry to molecular genetics, chemical ecology, and ecological genetics. None of the new specialties is considered more than a focus of research. Each is an industry of fresh ideas and advancing technology.
THE dream of intellectual unity was a product of the Enlightenment, an Icarian flight of the mind that spanned the seventeenth and eighteenth centuries. A vision of secular knowledge in the service of human rights and human progress, it was the West's greatest contribution to civilization. It launched the modern era for the whole world; we are all its legatees. Then -- astonishingly -- it failed.
Given the prospect of renewed convergence of the disciplines, it is of surpassing importance to understand both the essential nature of the Enlightenment and the weaknesses that brought it down. Both can be said to have been embodied in the life of the Marquis de Condorcet. No single event better marks the end of the Enlightenment than his death, on March 29, 1794. The circumstances were exquisitely ironic. Condorcet has been called the prophet of the Laws of Progress. By virtue of his towering intellect and visionary political leadership, he seemed destined to emerge from the French Revolution as the Jefferson of France. But in late 1793 and early 1794, as he was composing the ultimate Enlightenment blueprint, Sketch for a Historical Picture of the Progress of the Human Mind, he was instead a fugitive from the law, liable to a sentence of death by representatives of the cause he had so faithfully served. His crime was political: He was perceived to be a Girondist, a member of a faction found too moderate -- too reasonable -- by the radical Jacobins. Worse, he had criticized the constitution drawn up by the Jacobin-dominated National Convention. He died on the floor of a cell in the jail at Bourg-la-Reine, after being imprisoned by villagers who had captured him on the run. They would certainly have turned him over to the Paris authorities for trial. The cause of death is unknown. Suicide was ruled out at the time, but poison, which he carried with him, is nevertheless a possibility; so is trauma or heart attack. At least he was spared the guillotine.
The French Revolution drew its intellectual strength from men and women like Condorcet. It was readied by the growth of educational opportunity and then fired by the idea of the universal rights of man. Yet as the Enlightenment seemed about to achieve political fruition in Europe, something went terribly wrong. What seemed at first to be minor inconsistencies widened into catastrophic failures. Thirty years earlier Jean-Jacques Rousseau, in The Social Contract, had introduced the idea that was later to inspire the rallying slogan of the Revolution: "Liberty, Equality, Fraternity." But he had also invented the fateful abstraction of the "general will" to achieve these goals. The general will, he wrote, is the rule of justice agreed upon by assemblies of free people whose interest is only to serve the welfare of the society and of each person in it. When achieved, it forms a sovereign contract that is "always constant, unalterable, and pure." "Each of us puts his person and all his power in common under the supreme direction of the general will, and, in our corporate capacity, we receive each member as an indivisible part of the whole." Those who do not conform to the general will, Rousseau continued, are deviants subject to necessary force by the assembly. A truly egalitarian democracy cannot be achieved in any other way.
Robespierre, who led the Reign of Terror that overtook the Revolution in 1793, grasped this logic all too well. He and his fellow Jacobins understood Rousseau's necessary force to include summary condemnations and executions of all those who opposed the new order. Some 300,000 nobles, priests, political dissidents, and other troublemakers were imprisoned, and 17,000 died within the year. In Robespierre's universe the goals of the Jacobins were noble and pure. They were, as he serenely wrote in February of 1794 (shortly before he himself was guillotined), "the peaceful enjoyment of liberty and equality, the rule of that eternal justice whose laws have been engraved ... upon the hearts of men, even upon the heart of the slave who knows them not and of the tyrant who denies them."
Thus took form the easy cohabitation of egalitarian ideology and savage coercion that was to plague the next two centuries. The decline of the Enlightenment was hastened not just by tyrants who used it for justification but by rising and often valid intellectual opposition. Its dream of a world made orderly and fulfilling by free intellect had seemed at first indestructible, the instinctive goal of all men. The movement gave rise to the modern intellectual tradition of the West and much of its culture. Its creators, among the greatest scholars since Plato and Aristotle, showed what the human mind can accomplish. Isaiah Berlin, one of their most perceptive historians, praised them justly as follows: "The intellectual power, honesty, lucidity, courage, and disinterested love of the truth of the most gifted thinkers of the eighteenth century remain to this day without parallel. Their age is one of the best and most hopeful episodes in the life of mankind." But they reached too far, and their best efforts were not enough to create the sustained endeavor their vision foretold.
THIS, then, was the problem. Although reason supposedly was the defining trait of the human species, and needed only a little more cultivation to flower universally, it fell short. Humanity was not paying attention. Humanity thought otherwise. The causes of the Enlightenment's decline, which persist today, illuminate the labyrinthine wellsprings of human motivation. It is worth asking, particularly in this winter of our cultural discontent, whether the original spirit of the Enlightenment -- confidence, optimism, eyes to the horizon -- can be regained. And to ask in honest opposition, Should it be regained, or did it possess in its first conception, as some have suggested, a dark-angelic flaw? Might its idealism have contributed to the Terror, which foreshadowed the horrendous dream of the totalitarian state? If knowledge can be consolidated, so might the "perfect" society be designed -- one culture, one science -- whether fascist, communist, or theocratic.
The Enlightenment itself, however, was never a unified movement. It was less a determined, swift river than a lacework of deltaic streams working their way along twisted channels. By the time of the French Revolution it was very old. It emerged from the Scientific Revolution during the early seventeenth century and attained its greatest influence in the European academy during the eighteenth. Its originators often clashed over fundamental issues. Most engaged from time to time in absurd digressions and speculations, such as looking for hidden codes in the Bible and for the anatomical seat of the soul. The overlap of their opinions was nevertheless extensive and clear and well reasoned enough to bear this simple characterization: They shared a passion to demystify the world and free the mind from the impersonal forces that imprison it.
They were driven by the thrill of discovery. They agreed on the power of science to reveal an orderly, understandable universe and thereby lay an enduring base for free rational discourse. They thought that the perfection of the celestial bodies discovered by astronomy and physics could serve as a model for human society. They believed in the unity of all knowledge, individual human rights, natural law, and indefinite human progress. They tried to avoid metaphysics even as the flaws in and incompleteness of their explanations forced them to practice it. They resisted organized religion. They despised revelation and dogma. They endorsed, or at least tolerated, the state as a contrivance required for civil order. They believed that education and right reason would enormously benefit humanity. A few, like Condorcet, thought that human beings were perfectible and capable of shaping and administering a political utopia.