Part I Enlightenment The common sense of the eighteenth century, its grasp ofthe obvious facts of human suffering, and of the obvious demands of humannature, acted on the world like a bath of moral cleansing. --Alfred North Whitehead In the course of several decades giving public lectureson language, mind, and human nature, I have been asked some mighty strangequestions. Which is the best language? Are clams and oysters conscious? Whenwill I be able to upload my mind to the Internet? Is obesity a form ofviolence? But the most arresting question I have ever fieldedfollowed a talk in which I explained the commonplace among scientists thatmental life consists of patterns of activity in the tissues of the brain. Astudent in the audience raised her hand and asked me: "Why should I live?" The student''s ingenuous tone made it clear that she wasneither suicidal nor sarcastic but genuinely curious about how to find meaningand purpose if traditional religious beliefs about an immortal soul are underminedby our best science. My policy is that there is no such thing as a stupidquestion, and to the surprise of the student, the audience, and most of allmyself, I mustered a reasonably creditable answer. What I recallsaying--embellished, to be sure, by the distortions of memory and l''esprit del''escalier, the wit of the staircase--went something like this: In the very act of asking that question, you are seekingreasons for your convictions, and so you are committed to reason as the meansto discover and justify what is important to you. And there are so many reasonsto live! As a sentient being, you have the potential to flourish.You can refine your faculty of reason itself by learning and debating.

You canseek explanations of the natural world through science, and insight into thehuman condition through the arts and humanities. You can make the most of yourcapacity for pleasure and satisfaction, which allowed your ancestors to thriveand thereby allowed you to exist. You can appreciate the beauty and richness ofthe natural and cultural world. As the heir to billions of years of lifeperpetuating itself, you can perpetuate life in turn. You have been endowedwith a sense of sympathy--the ability to like, love, respect, help, and showkindness--and you can enjoy the gift of mutual benevolence with friends, family,and colleagues. And because reason tells you that none of this isparticular to you, you have the responsibility to provide to others what youexpect for yourself. You can foster the welfare of other sentient beings byenhancing life, health, knowledge, freedom, abundance, safety, beauty, andpeace. History shows that when we sympathize with others and apply ouringenuity to improving the human condition, we can make progress in doing so,and you can help to continue that progress.

Explaining the meaning of life is not in the usual jobdescription of a professor of cognitive science, and I would not have had thegall to take up her question if the answer depended on my arcane technicalknowledge or my dubious personal wisdom. But I knew I was channeling a body ofbeliefs and values that had taken shape more than two centuries before me andthat are now more relevant than ever: the ideals of the Enlightenment. The Enlightenment principle that we can apply reason andsympathy to enhance human flourishing may seem obvious, trite, old-fashioned. Iwrote this book because I have come to realize that it is not. More than ever,the ideals of reason, science, humanism, and progress need a wholehearted defense.We take its gifts for granted: newborns who will live more than eight decades,markets overflowing with food, clean water that appears with a flick of afinger and waste that disappears with another, pills that erase a painfulinfection, sons who are not sent off to war, daughters who can walk the streetsin safety, critics of the powerful who are not jailed or shot, the world''sknowledge and culture available in a shirt pocket. But these are humanaccomplishments, not cosmic birthrights. In the memories of many readers ofthis book--and in the experience of those in less fortunate parts of theworld--war, scarcity, disease, ignorance, and lethal menace are a natural partof existence.

We know that countries can slide back into these primitive conditions,and so we ignore the achievements of the Enlightenment at our peril. In the years since I took the young woman''s question, Ihave often been reminded of the need to restate the ideals of the Enlightenment(also called humanism, the open society, and cosmopolitan or classicalliberalism). It''s not just that questions like hers regularly appear in myinbox. ("Dear Professor Pinker, What advice do you have for someone who hastaken ideas in your books and science to heart, and sees himself as a collectionof atoms? A machine with a limited scope of intelligence, sprung out of selfishgenes, inhabiting spacetime?") It''s also that an obliviousness to the scope ofhuman progress can lead to symptoms that are worse than existential angst. Itcan make people cynical about the Enlightenment-inspired institutions that aresecuring this progress, such as liberal democracy and organizations ofinternational cooperation, and turn them toward atavistic alternatives. The ideals of the Enlightenment are products of humanreason, but they always struggle with other strands of human nature: loyalty totribe, deference to authority, magical thinking, the blaming of misfortune onevildoers. The second decade of the 21st century has seen the rise of politicalmovements that depict their countries as being pulled into a hellish dystopiaby malign factions that can be resisted only by a strong leader who wrenchesthe country backward to make it "great again." These movements have beenabetted by a narrative shared by many of their fiercest opponents, in which theinstitutions of modernity have failed and every aspect of life is in deepeningcrisis--the two sides in macabre agreement that wrecking those institutions willmake the world a better place.

Harder to find is a positive vision that seesthe world''s problems against a background of progress that it seeks to buildupon by solving those problems in their turn. If you still are unsure whether the ideals ofEnlightenment humanism need a vigorous defense, consider the diagnosis ofShiraz Maher, an analyst of radical Islamist movements. "The West is shy of itsvalues--it doesn''t speak up for classical liberalism," he says. "We are unsureof them. They make us feel uneasy." Contrast that with the Islamic State, which"knows exactly what it stands for," a certainty that is "incrediblyseductive"--and he should know, having once been a regional director of thejihadist group Hizb ut-Tahrir.1 Reflecting on liberal ideals in 1960, not long after theyhad withstood their greatest trial, the economist Friedrich Hayek observed, "Ifold truths are to retain their hold on men''s minds, they must be restated inthe language and concepts of successive generations" (inadvertently proving hispoint with the expression men''s minds). "What at one time are their mosteffective expressions gradually become so worn with use that they cease tocarry a definite meaning.

The underlying ideas may be as valid as ever, but thewords, even when they refer to problems that are still with us, no longer conveythe same conviction."2 This book is my attempt to restate the ideals of theEnlightenment in the language and concepts of the 21st century. I will firstlay out a framework for understanding the human condition informed by modernscience--who we are, where we came from, what our challenges are, and how we canmeet them. The bulk of the book is devoted to defending those ideals in adistinctively 21st-century way: with data. This evidence-based take on theEnlightenment project reveals that it was not a naïve hope. The Enlightenmenthas worked--perhaps the greatest story seldom told. And because this triumph isso unsung, the underlying ideals of reason, science, and humanism areunappreciated as well. Far from being an insipid consensus, these ideals are treatedby today''s intellectuals with indifference, skepticism, and sometimes contempt.

When properly appreciated, I will suggest, the ideals of the Enlightenment arein fact stirring, inspiring, noble--a reason to live. Chapter 1 Dare to Understand! What is enlightenment? In a 1784 essay with that questionas its title, Immanuel Kant answered that it consists of "humankind''s emergencefrom its self-incurred immaturity," its "lazy and cowardly" submission to the"dogmas and formulas" of religious or political authority.1 Enlightenment''smotto, he proclaimed, is "Dare to understand!" and its foundational demand isfreedom of thought and speech. "One age cannot conclude a pact that wouldprevent succeeding ages from extending their insights, increasing their knowledge,and purging their errors. That would be a crime against human nature, whoseproper destiny lies precisely in such progress."2 A 21st-century statement of the same idea may be found inthe physicist David Deutsch''s defense of enlightenment, The Beginning ofInfinity. Deutsch argues that if we dare to understand, progress is possible inall fields, scientific, political, and moral: Optimism (in the sense that I have advocated) is thetheory that all failures--all evils--are due to insufficient knowledge.Problems are inevitable, because our knowledge will always be infinitely farfrom complete.

Some problems are hard, but it is a mistake to confuse hardproblems with problems unlikely to be solved. Problems are soluble, and eachparticular evil is a problem that can be solved. An optimistic civilization isopen and not afraid to innovate, and is based on traditions of criticism. Itsinstitu.