“The best of all possible worlds” is a simplistic expression stemming from the philosopher Gottfried Wilhelm Leibniz’s complex 1710 “Essays of Theodicy.” Voltaire lampooned it in his “Candide,” when he had his character Pangloss declare that “all is for the best in the best of all possible worlds.”

This is the background of the concerted effort that is now underway to promote a new optimism, armed with data and also backed by philosophy.

It was around the year 2000, at the height of the post-Cold War era and the rise of globalization, when the optimists first staged a comeback. However, the momentum they had hoped for did not materialize.

Jihadist terrorism, notably on Sept. 11, 2001, and the economic and financial crisis following the collapse of Lehman Brothers, 10 years ago this fall, stood in their way.

One voice at the forefront of the new outbreak of optimism, accompanied by publications of serious academic quality, is the cognitive scientist Steven Pinker. In 2011, his book “The Better Angels of Our Nature” focused on using data to show that the world has never been less violent.

Now, he has gone further with a new book, “Enlightenment Now: The Case for Reason, Science, Humanism and Progress.” Now, the claim extends to many other milestones humanity has reached. These range from life expectancy at birth (which, measured on a worldwide basis, has risen from 30 years at the time of the Enlightenment to 71 today) to health.

Pinker is delighted to point out that, according to Wikipedia, “smallpox was” — using in the past tense — “a serious infectious disease.”

This portrait of humanity is also supported by “Factfulness: Ten Reasons We’re Wrong About the World — and Why Things Are Better Than You Think,” by the late Swedish physician Hans Rosling, written in conjunction with Anna and Ola Rosling.

When simple questions are posed about global trends — such as what percentage of the world’s population lives in poverty? How many girls complete their schooling? — Rosling argues that both lay people and the elites at the Davos Forum consistently come up with the wrong answers.

They are so wrong, he claims, that a chimpanzee choosing answers at random would reliably outperform the gurus, journalists, Nobel Prize winners and investment bankers. He sets out the “fight against devastating global ignorance” as a mission of overriding importance. He billed himself not as an optimist but a “possibilist.”

IQ scores have risen worldwide by three points in a decade. The number of people using mobile phones exceeds 5 billion out of a global population of 7.6 billion. Naturally, there is still a long way to go, and the pressing need to meet the United Nation’s 17 Sustainable Development Goals by 2030 proves it.

Pinker sets out 15 ways of measuring progress in human welfare, and he documents them. He does not discount the idea that humans are destroying the Earth and that therefore progress is not sustainable. He just thinks that solutions will be sought and found.

Pinker argues that “reason is non-negotiable,” which does not mean that human beings are perfectly rational. He possibly errs on the side of utilitarianism and positivity.

And his idea of the Enlightenment, while based on Kant, is ultimately not particularly Kantian because of the lack of centrality given to critical rationality and the sense of “maturity” favored by the philosopher from Konigsberg (nowadays the Russian enclave of Kaliningrad).

In his new book, Pinker gives more weight to this critique, and to what it entails: That reason, science and humanism drive progress and that this is real, albeit not inexorable. He continues to reject fatalism outright, whether in terms of coexistence among humans or between humans and new machines, which hold no fears for him.

Pinker identifies some things that run counter to the Enlightenment, essentially religious faith (he is a “secular humanist,” as John Gray would say), the idea that people are the “replaceable cells of a superorganism” (collectivism and communitarianism), what he terms the “romantic green movement,” which “subordinates human interests to a transcendent entity,” a focus on the “decline” of civilization, and opposition to science on the grounds that it undermines some of the preceding elements.

Pinker also includes populist movements — he acknowledges that the book was written essentially before Trump’s victory in his home country — the emergence of authoritarianism, global warming and the return of the nuclear issue.

The general direction of the Enlightenment has drifted off course. Pinker’s attempt to restore it is much to be welcomed, although not everything is as solvable as presented by the author, who thinks some problems will solve themselves.

Whether by their actions (or omissions), humans sometimes create problems so complex that they are incapable of solving them. Many critics of his new book agree that he continues seeing the glass as half full, rather than half empty.

Whereas Pinker highlights the global coming together of societies in terms of wealth, the “great convergence” that is revolutionizing the world, he underestimates or rejects one of the major preoccupations of our age: Inequality within societies, which has particularly grown since the 1980s, on the grounds that it is not “a fundamental component of wellbeing.”

Pinker is more interested in poverty reduction. He criticizes those intellectuals who are labeled “progressives” but who, he claims, actually “hate” progress. Pinker believes in progress.

Voltaire’s Candide, of course, ended up concluding that optimism was nothing but a mania for insisting that “everything goes well, when things are going badly.” Pinker, however, allows us to realize that many things are going much better, even though we are not in the best of all possible worlds.

As he himself puts it, “the problems faced by the whole planet are formidable.” He is not in radical disagreement with Voltaire. He thinks that nothing is guaranteed in this unstable world, but that many things have improved. Setting out from this recognition, Pinker believes they can and should be improved much more.

Mario Benedetti, the Uruguayan journalist, novelist and poet, famously said that “a pessimist is a well-informed optimist.” Pinker would beg to differ, with data. In any event, in the debate between optimism and pessimism it is important not to downplay realism.

Andres Ortega is a senior research fellow at Royal Elcano Institute, Spain’s main think tank in international affairs, in charge of global governance. www.theglobalist.com