‘Tell people there’s an invisible man in the sky who created the universe,” the comedian George Carlin once observed, “and the vast majority will believe you. Tell them the paint is wet, and they have to touch it to be sure.”

Carlin’s quip is one of many in Steven Pinker’s “Rationality,” an engaging analysis of the highest of our faculties and perhaps (ironically) the least understood. Rational thinking, as Mr. Pinker defines it, is “the ability to use knowledge to attain goals.” True, he notes, those goals themselves—not...

‘Tell people there’s an invisible man in the sky who created the universe,” the comedian George Carlin once observed, “and the vast majority will believe you. Tell them the paint is wet, and they have to touch it to be sure.”

Carlin’s quip is one of many in Steven Pinker’s “Rationality,” an engaging analysis of the highest of our faculties and perhaps (ironically) the least understood. Rational thinking, as Mr. Pinker defines it, is “the ability to use knowledge to attain goals.” True, he notes, those goals themselves—not just material sustenance or health but love, kindness and just a little crazy fun now and then—need not be rationally based. But we must use reason to choose among them when they conflict. Nor do the means to attain those goals always have to be rational; custom, tradition and taboo all have a role.

Mr. Pinker’s main concern lies with the many ways we frustrate our pursuit by making irrational mistakes about reality. Not only are we prone to believe in an invisible man in the sky—Mr. Pinker has little time for literal religious belief—but we are suckers for the “mythological,” many of us believing in ghosts and other supernatural “woo-woo.”

We are also “motivated” in our use of reason—motivated, that is, to feel good—and so lend credence to invisible forces within nature. Thus we may believe that “everything happens for a reason” or, on a grander scale, that a Hegelian force moves history in a progressive direction. Such worldviews satisfy our craving to believe that a setback now will lead to something good later on.

Even so, they are bad for us, Mr. Pinker notes, since they can lull us into an unjustified complacency about our life. And why do we touch paint we are told is wet? It’s because we are, Mr. Pinker says, “myopic.” We give enormous street cred to the way the world appears to us, to evidence that’s immediately available to our five senses—hence the “availability” bias diagnosed by Daniel Kahneman and Amos Tversky—and we play down distant sources of information. We overestimate the risks of certain activities because rare accidents and catastrophes are vividly dramatic and breathlessly reported; meanwhile, we ignore “routine” risks that are in fact much higher: e.g., these days, covering our face with a mask while driving alone in a car but stepping on the gas to run a yellow light.

And we are also, Mr. Pinker says, “mysiders.” We devalue the statements of those outside our own group: Just as we discount it if a stranger posts a sign that says “wet paint” (we touch the sign to confirm the claim), we dismiss it when a stranger provides good reasons for us to rethink our political or social views.

And yet, for all such irrationalities, Mr. Pinker observes, we humans have somehow managed to deploy our faculty of reason to develop language and mathematics, cure diseases, and engineer legal and governmental systems. Over time, traits such as humility and a sense of our own fallibility have made us willing to submit our beliefs to “the trials of reason” through peer review or public debate, enabling rationality to “conquer the universe of belief” and push irrationality “to the margins.”

True, Mr. Pinker notes, those who think that their rational faculties have conquered the universe of belief are, often, the least humble. He calls out academics, lacking any sense of fallibility about their own purported truths, who stifle debate on college campuses. But, Mr. Pinker concludes, there is a way forward. We should use education to “instill” humility as a kind of life skill, much as we have done with literacy and numeracy, thus giving human reason the widest possible berth to converge on the truth.

Mr. Pinker tells a compelling story. But competing with it is a counter-narrative: It’s not so much that humility generates the greatest feats of reason as that those who have accomplished such feats are the most humble. On this account, human reason doesn’t march in a linear progression, as Mr. Pinker suggests, bringing more and more of reality under its ambit and leaving less and less remaining outside. Rather reason discovers, as it advances, the limits of its comprehension, making the unknowable appear ever larger: an experience that induces humility.

Mr. Pinker doesn’t discuss physics. But many physicists now wonder whether reason has the capacity to penetrate inside the smallest, quantum bits of the universe or to take us outside of the universe as a whole so as to explain its origins or determine whether ours might be part of a multiverse. “Who says,” the physicist Neil Turok asks, that “we have any right to understand the universe anyway?”

Nor does Mr. Pinker discuss the possible limits of reason when it comes to comprehending the world within our heads. Yet here too philosophers like Colin McGinn claim that we are “bang up against the limits of our capacity to understand” the nature of consciousness; any further understanding would require us to somehow get outside the mind, pondering it from an Archimedean point that’s unavailable to us. Similarly, reason has trouble getting us entirely inside the mind. There comes a limit where language itself, as Wittgenstein noted, can no longer convey the full interiority of another person’s thoughts and feelings. He counseled a kind of modest reticence: “That whereof we cannot speak, thereof we must remain silent.”

Intriguingly, those of us who are not great thinkers confront similar limitations when it comes to using our rational faculty, as Mr. Pinker’s examples show. But because we are less able to see beyond them, we end up feeling self-certainty instead of humility. Myopia makes it difficult to get out of our own minds—to accept that there might be more than what’s readily apparent—while myside bias means that we often fail to see the mental interiority, the feelings and challenges of those with whom we differ. Motivated reasoning encourages us to view the universe as governed by internal forces designed to favor our own particular hopes and dreams, while mythological reasoning leads us to see it as governed by our own favored external forces, our own particular deities and prophets.

One great Catch-22 of our species is that, while humility is necessary for reason to flourish, as Mr. Pinker rightly says, reason is ultimately necessary for humility to take root. If education is the answer, perhaps it lies in exposing students to the greatest accomplishments of human reason in the arts and sciences. Humility should emerge within us organically, as it always has for humanity’s farthest-reaching reasoners.

—Mr. Stark is the author of “The Consolations of Mortality.”