If you haven’t encountered any reviews of Harvard psychologist Steven Pinker’s new bestseller Enlightenment Now—which would be amazing, given how many there have been—don’t worry. I can summarize them in two paragraphs.

The positive ones say Pinker argues convincingly that we should be deeply grateful for the Enlightenment and should put our stock in its legacy. A handful of European thinkers who were born a few centuries ago set our species firmly on the path of progress with their compelling commitment to science, reason, and humanism (where humanism means “maximizing human flourishing”). Things have indeed, as Pinker documents in great detail, gotten better in pretty much every way—materially, morally, politically—since then. And if we stay true to Enlightenment values, they’ll keep getting better.

The negative reviews say things like this: Pinker attributes too much of our past progress to Enlightenment thought (giving short shrift, for example, to the role of Christian thinkers and activists in ending slavery); his faith in science and reason is naive, given how often they’ve been misused; his assumption that scientifically powered progress will bring happiness betrays a misunderstanding of our deepest needs; his apparent belief that secular humanism can fill the spiritual void left by rationalism’s erosion of religion only underscores that misunderstanding; and so on. In short: In one sense or another, Pinker overdoes this whole enlightenment thing.

My own problem with the book is the sense in which Pinker underdoes the enlightenment thing. In describing the path that will lead humankind to a bright future, he ignores the importance of enlightenment in the Eastern sense of the term. If the power of science and reason aren’t paired with a more contemplative kind of insight, I think the whole Enlightenment project, and maybe even the whole human experiment, could fail.

If you fear I’m heading in a deeply spiritual or excruciatingly mushy direction—toward a sermon on the oneness of all beings or the need for loving kindness—I have good news: I’ve delivered such sermons, but this isn’t one of them. Eastern enlightenment has multiple meanings and dimensions, and some of those involve more logical rigor than you might think. In the end, an Eastern view of the mind can mesh well with modern cognitive science—a fact that Pinker could have usefully pondered before writing this book.

Pinker’s argument is more sophisticated than some caricatures of it would have you believe. In particular, he recognizes the big kink in his famously optimistic take on the future: Though reason can help us solve the problems facing humankind, our species isn’t great at reasoning. We have “cognitive biases”—like, for example, confirmation bias, which inclines us to notice and welcome evidence that supports our views and to not notice, or reject, evidence at odds with them. Remember how unseasonably warm it was a few months ago? The answer may depend on your position on the climate change question—and that fact makes it hard to change people’s minds about climate change and thus build the consensus needed to address the problem.

Pinker also understands that cognitive biases can be activated by tribalism. “We all identify with particular tribes or subcultures,” he notes—and we’re all drawn to opinions that are favored by the tribe.

So far so good: These insights would seem to prepare the ground for a trenchant analysis of what ails the world—certainly including what ails an America now famously beset by political polarization, by ideological warfare that seems less and less metaphorical.

But Pinker’s treatment of the psychology of tribalism falls short, and it does so in a surprising way. He pays almost no attention to one of the first things that springs to mind when you hear the word “tribalism.” Namely: People in opposing tribes don’t like each other. More than Pinker seems to realize, the fact of tribal antagonism challenges his sunny view of the future and calls into question his prescriptions for dispelling some of the clouds he does see on the horizon.

I’m not talking about the obvious downside of tribal antagonism—the way it leads nations to go to war or dissolve in civil strife, the way it fosters conflict along ethnic or religious lines. I do think this form of antagonism is a bigger problem for Pinker’s thesis than he realizes, but that’s a story for another day. For now the point is that tribal antagonism also poses a subtler challenge to his thesis. Namely, it shapes and drives some of the cognitive distortions that muddy our thinking about critical issues; it warps reason.