Caroline Winterer is a historian at Stanford University and the author of “American Enlightenments: Pursuing Happiness in the Age of Reason.”

If 2017 was a rough year for you, look no further than Steven Pinker’s engaging new book, “Enlightenment Now,” to cheer you up. Conceived before Donald Trump even announced his candidacy, it could not have been better timed to clarify — and, for some, refute — the habits of mind that brought Trump and the GOP to power.

Pinker hopes to revive the values of the Enlightenment by making a case for reason, science, progress and fact-based argument. He musters an army of numbers to vanquish a host of enemies: religion, conservatism, nationalism, tribalism, Marxism, authoritarian populism, postmodern theorists, Nietzsche and many more.

Pinker’s launching pad is the Enlightenment, when many things started improving for homo sapiens. The age that used reason to crush superstition culminates in the cheerful graphs that adorn this book. Going up are life expectancy, calories consumed, gross world product and incomes. Going down are infant and maternal mortality, death from famine, starvation, extreme poverty, social spending, and even the loneliness of U.S. college students.

“Enlightenment Now,” by Steven Pinker (Viking)

His conclusion: Chin up! “Everything is amazing!” Pinker declares. “And none of us are as happy as we ought to be, given how amazing our world has become.” Even when Americans report that they are less happy, they also report that life is more exciting. Progress is everywhere, even when it doesn’t look like progress.

A psychology professor at Harvard, Pinker is as interested in how to think as what to think. Worried about the big, global, existential threats — overpopulation, resource depletion, nuclear war and climate change? Pinker urges us first to change the way we think about them. They are not apocalypses in waiting but problems to be solved. He cites a study showing that people may be more likely to acknowledge a problem when they think it’s solvable than when they are frozen by fear.

What Pinker doesn’t like are progress deniers. They can’t just be written off as feckless grumblers because their gloom and doom paralyze us, imperiling our very survival. He spreads the blame broadly. The media feeds our tendency toward availability bias: People estimate the probability of an event by how easily some version of it springs to mind. One graph’s steeply plunging line shows the deteriorating tone of the news since 1945. Right-wing politicians ignore the facts of science. The left, pontificating from universities and high-brow media, trafficks in “a philistine indifference to science.” Some professors teach undergraduates that “science does not converge on the truth.”

To the rescue comes the Enlightenment. Pinker’s book is the latest in a long line to summon the Enlightenment to defend us against looming political threats. From the gloomy precipice of 1930s Germany, the philosopher Ernst Cassirer called upon the Enlightenment to block the ominous rise of Nazism and fascism. During the Cold War, Americans looked backward 200 years to what they christened “the American Enlightenment” — a new coinage of the post-World War II era — as an ideological bomb shelter of freedom, democracy and Christianity that would shield them from the godless collectivism brewing in the Soviet Union.

Each generation connects us to the Enlightenment in new ways. To paraphrase Voltaire, if the Enlightenment didn’t exist, we would have to invent it.

The Enlightenment is a notoriously fuzzy concept — pretty much every historian has their own version — so it is no criticism of Pinker to say that his Enlightenment is a kitchen pantry for the modern ideas that interest him. Its philosophers and scientists materialize when their ideas foreshadow modernity. Baruch Spinoza, David Hume, Adam Smith and the French Encyclopédistes were “cognitive and social psychologists ahead of their time,” Pinker writes.

Other parts of the Enlightenment — those that don’t clearly link to the “Now” of Pinker’s title — stay locked in the cupboard. Some ideas, perfectly reasonable in their own era, have by now disappeared or been proved false. Viewed from today, Thomas Jefferson was a one-man error factory. He argued, incorrectly, that fossil seashells could be found on mountaintops because they leaked into those shapes from the surrounding rocks. He erroneously maintained that the ancient Carthaginians were the original peoples of the New World. But Jefferson’s scientific theories, based on data and reason, also belong to the curious, delightful and often alien world of the 18th century.

And some Enlightenment ideas have changed so drastically that we don’t even recognize them today. Take happiness. In the 18th century, happiness often meant what John Adams called public or social happiness. Pursuing happiness meant first securing the state against external threats (like invading armies) or dangers on the home front (like unhinged demagogues). The opposite of public happiness wasn’t sadness: It was tyranny, anarchy and the rupture of the social fabric. Only with public happiness secured could people pursue private or personal happiness — those nooks and crannies of our lives that we fill with friends and family.

Today we remember only the private meaning of happiness, and we misinterpret the Declaration of Independence accordingly. The self-help industry equates happiness with personal well-being and self-fulfillment. This shrinks human happiness to the domain of psychologists and life coaches. By contrast, public happiness — the happiness of the Declaration of Independence — is every citizen’s concern and the first civic duty of legislators and presidents. Viewed from the Enlightenment, happiness today would be increasing or decreasing depending on which kind you were pursuing, public or private. Maybe we are personally happier glued to our phones, since they help us connect with our friends. But how are we scoring on public happiness in the age of Trump?

Pinker is far more interested in what connects the Enlightenment to our predicaments today. He offers three links, fully acknowledging that they were unknown in the 18th century: entropy (the Second Law of Thermodynamics), evolution and information. Pinker uses them to tie 18th-century ideas to 21st-century physics, biology and cognitive psychology. He wants to draw a rising line of human flourishing from 200 years ago to now. He is an unquenchable optimist, just like Jefferson’s friend Pierre Samuel du Pont de Nemours, who like a good Frenchman turned to escargots to describe humanity’s steady ascent toward a sunny tomorrow. “We are snails and we have a mountain range to climb! By God, we must climb it!” Like the optimists of the Enlightenment, Pinker calls the climb “progress.”

And progress is where Pinker may be launching his most controversial argument. Is progress a law of nature, akin to the laws of physics? Or is it an interpretive frame, invented by human beings in the 18th century to crowd out problematic alternatives for the fate of humanity — say, the depressing Fall described in Genesis, or the cyclical theories of inevitable political rise and decline current among the Greeks and Romans? Compared with these two chestnuts, progress is the new kid on the block.

Pinker wants progress to be a law of nature, what he calls a “reality” that numbers and charts can show. Yet he finally settles on surprisingly religious arguments about progress. Progress can feel like an “arc bending toward justice,” a phrase he draws from the Rev. Martin Luther King Jr. Pinker concludes the book with words that may both stir and puzzle readers by blending science and religion. The story of human progress is ultimately “spiritual,” he writes. We are “blessed” with resources that offer a kind of “redemption.”

Are there no alternatives to progress for interpreting history? Charles Darwin offered one: adaptation. Darwin’s world was about getting by, not progressing. If — or rather, when — the environment changes, a helpful trait can become harmful. It’s all about trade-offs.

Pinker speaks fondly of the gifts of the Enlightenment. And there were many. But the Enlightenment also gave us habits of mind, among them the habit of thinking that the human experience can be aligned along a single axis of progress. Pinker’s gift is to challenge us not only to update the Enlightenment but to think beyond it.

Enlightenment Now
The Case for Reason, Science, Humanism, and Progress

By Steven Pinker

Viking. 556 pp. $35