Logic: Why it matters and how to be better at it

Misinformation and disinformation are growing threats in our society. But, argues Harvard professor Steven Pinker, we can use our brains to provide certainty in chaotic times. By Danyl McLauchlan.

Maybe we’re just not thinking clearly. Maybe the problems in our lives and the chaos of the world have the same root cause: ignorance, folly, a global pandemic of unreason. And maybe the cure to all this foolishness lies within our own minds. Maybe we can heal ourselves, and everything will come right if we stop and think things through calmly, logically and rationally.

Back in 2011, Steven Pinker, Harvard psychologist and the eminent author of many bestselling books on language and the mind, swerved out of his academic lane to write The Better Angels of Our Nature, a polemical work of interdisciplinary social science. It argued that although many of us believed the world was growing ever more violent and dangerous, if you looked at the data the reverse was true: people living in developed nations enjoyed a level of peace that was unprecedented in human history. He cited archaeological studies showing that most pre-modern societies were characterised by constant warfare and endemic violence.

We were wrong about the past, Pinker argued, wrong about the modern world and wrong about the future, which would be utopian rather than dystopian. And, he explained, our safe and happy lives were all thanks to the modern state, free-market capitalism, increased literacy and scientific rationalism.

These were controversial claims, especially to those who believe capitalism, rationalism and so on are evil and destroying the planet. Scholars are still fighting about Pinker’s thesis 10 years on, and in 2018, he doubled down, publishing Enlightenment Now: the case for reason, science, humanism, and progress. It’s an even more sweeping and controversial argument that actually everything is getting better: humans as a species are happier, healthier, safer and better off than ever before.

For some, this felt a little hard to swallow, even before Covid, the rise of populist authoritarianism and the latest announcements of climate doom. So Pinker’s new work, Rationality: what it is, why it seems scarce, why it matters, is – slightly – less optimistic. Yes, he admits, there are problems in the world. But they’re caused by a lack of rationality.

But what is rationality? Pinker shies away from a specific definition. To him, rationality is both “knowledge about the world” and “a kit of cognitive tools that can attain particular goals in particular worlds”. And he insists that it isn’t specific to any single culture, inviting us to consider the rational deductions of the San, a hunter-gatherer society in the Kalahari Desert, who use critical thinking and conditional probabilities and distinguish cause from effect when hunting and trapping animals.

The San deploy this rationality to track the fleeing animals from their hoofprints, effluvia and other spoors. Hunters distinguish dozens of species by the shapes and spacing of their tracks, aided by their grasp of cause and effect. They may infer that a deeply pointed track comes from an agile springbok, which needs a good grip, whereas a flat-footed track comes from a heavy kudu, which has to support its weight. They use these categories to make syllogistic deductions: steenbok and duiker can be run down in the rainy season because the wet sand forces open their hooves and stiffens their joints; kudu and eland can be run down in the dry season because they tire easily in loose sand. It’s the dry season and the animal that left these tracks is a kudu: therefore, this animal can be run down.

Dealing with randomness

So how do we think like the San and track our own spoors through the wet sands of life? How do we acquire more logical certainty about the world? Well, somewhat paradoxically, we begin by abandoning certainty.

We should think probabilistically. Probably.

It would be nice if we could use rationality – logic, statistics, experience – to predict the future: to know the outcomes of political events, weather patterns or economic trends. But the world is not so obliging. Most of the systems humans want to predict are chaotic, meaning that tiny changes can cause unpredictably large effects. A butterfly flapping its wings causing a storm in another part of the world is the classic example, but the problem of uncertainty affects everything from election results to Covid modelling and the timing and severity of our lockdowns. Pinker writes: “An essential part of rationality is dealing with randomness in our lives and uncertainty in our knowledge.”

Bayesian reasoning

Te Pūnaha Matatini is the Auckland University-based Centre of Research Excellence that advises the Government on its Covid response. It’s a transdisciplinary team founded by physics professor Shaun Hendy. Its speciality is modelling and forecasting the behaviour of complex systems, and in many ways it’s a model of the framework at the heart of Pinker’s book.

When the Delta variant of Covid-19 was detected in Auckland on August 17, Hendy and his team needed to estimate the size of the actual outbreak. “We maintain a bunch of assumptions about the likelihood of someone with symptoms going to get tested and how rapidly the Delta variant might spread,” says Hendy. “These are informed by data. For example, the number of tests in the past week and information from overseas on Delta outbreaks. We also need to make an assumption about when the virus was first introduced, something that is often available in a day or two thanks to whole genome sequencing.”

But even with all this information, every simulated outbreak will be different, just as it is in the real world. For example, for the August 17 outbreak, the model simulated 10,000 outbreaks, extracted the median outcome and took into account how confident you could be that the result was accurate. The median was estimated to be about 100 cases.

However, it also needed to encompass the fact that some large superspreading events could have occurred. And some outbreaks could turn out to be near misses.

“Within a week, it became apparent that a big superspreading event had taken place at the Assembly of God church, while the Covid case who turned up on August 17 was found not to have passed it on to anyone on the Coromandel Peninsula,” says Hendy. “At this point, we have to reset our initial expectations to match what had really taken place amongst the range of possible outcomes that were still on the table from day one. Hence, our estimate of cases on August 17 shifts from 100 to 300-400.”

This is the process known as Bayesian reasoning, which is prized by rationalists. You make predictions about the world based on assumptions known as “priors”, test them against reality and then “update your priors”, if or when your assumptions are wrong.

This may sound simple, but it’s not the way most of us think and act in the world. Instead, we practise what the legal academic Dan Kahan calls “motivated reasoning”, in which we make overconfident judgments about reality and then discount any new information that contradicts us. Pinker notes, rather bleakly: “We evolved not as intuitive scientists but as intuitive lawyers.”

Having better arguments

Because of cognitive bias we have to change our minds when the facts change, as the famous John Maynard Keynes quote goes.

Pinker believes that most moral progress happens through argument. “My greatest surprise in making sense of moral progress is how many times in history the first domino was a reasoned argument.

“A philosopher wrote a brief, which laid out arguments on why some practice was indefensible, or irrational, or inconsistent with values that everyone claimed to hold. The pamphlet or manifesto went viral, was translated into other languages, was debated in pubs and salons and coffeehouses, and then influenced leaders, legislators, and popular opinion.

“Eventually, the conclusion was absorbed into the conventional wisdom and common decency of a society, erasing the tracks of the arguments that brought it there.”

Few people today feel the need to argue why slavery is wrong, or public disembowelment, for example. “Yet exactly those debates took place centuries ago.”

But just as changing our minds is a skill we need to learn, so is persuading, and being persuaded, through argument. There are many well-known traps we fall into when we agree to disagree .

Trust or betrayal?

Most people have heard of “the prisoner’s dilemma”, the most famous game in the field of game theory – a suite of thought experiments and mathematical tools to model strategic interactions between rational decision makers. Here is Pinker’s description of the dilemma:  “A prosecutor detains partners in crime in separate cells, lacks the evidence to convict them, and offers them a deal. If one agrees to testify against the other, he will go free and his partner will go to prison for 10 years. If each rats out the other, they both get six years. If they stay true to the partnership and keep mum, she can only convict them on a lesser charge and they will serve six months.”

What are we supposed to do with this? The best way to view the dilemma is as a modern fable or a mathematical parable. Just as The Boy Who Cried Wolf isn’t really about a boy and a wolf, the prisoner’s dilemma isn’t really about prisoners. It’s a metaphor for competition, co-operation and trust.

The key principle is that for each prisoner, the rational option is to testify against their accomplice. But if they both testify, then they both go to prison. To avoid that they need to co-operate, which requires them to trust one another. But if you think the other prisoner trusts you, your rational option is to defect. And so is theirs.

Once you get the logic of the dilemma, you see it everywhere.

One of the best movies of 2019 was Noah Baumbach’s Marriage Story. Scarlett Johansson and Adam Driver play a married couple getting a divorce, and they hire lawyers to tear one another to shreds because each can’t trust the other not to do so. That’s the prisoner’s dilemma.

Nations around the world are failing to meet their obligations to reduce carbon emissions because they can’t be sure all the other nations won’t also defect from the agreements they’ve signed up to. Classic prisoner’s dilemma.

Pandemic behaviour

Rationalism is often seen as cold, logical and inhuman. And sometimes it is. But game theory shows that even if you map human interactions with mathematics, you quickly wind up back in the messy, emotional world of loyalty, trust and betrayal.

It also reveals a powerful tension between what’s best for us as rational individuals and what’s best for us collectively. Because it even dictates how we behave during a pandemic. Do you wear a mask, get vaccinated and obey the lockdown laws, or do you defect and do whatever you want and hope that everyone else follows the rules? And what happens in a society in which everyone does this?

Much of Western philosophy for the past 200 years has been an extended fight about rationality. Is it saving the planet or destroying it? Are mathematics, logic and science the only ways to accurately perceive the world? Or do they conceal as much as they reveal?

To Pinker, these critiques are simply wrong – woke garbage and postmodern nonsense. He is fervently, almost irrationally, pro-reason. But even he concedes that rationalism is something that happens at the cultural or institutional level, concluding, “not even the most rational among us is bias-free. Instead [our institutions] have channels of feedback and knowledge aggregation that make the whole smarter than any of its parts.”

Hendy agrees, noting the importance of having a diverse group of voices who scrutinise both the evidence before them and also “the very questions for which evidence is being sought”.

Lessons of 1918

Early in the pandemic response, his team considered the impact of Covid-19 on Māori. “On the one hand, it was tempting to assume that the impacts would be light, because Covid is much worse in older people and the Māori population is relatively young.

“However, one of our Māori board members had his iwi’s mātauranga from the 1918 pandemic and he urged us to not make this assumption, given the consequences.
“Within a few weeks, evidence started to emerge from the UK that comorbidities were a significant risk factor for fatalities, and because Māori receive poorer healthcare, they were indeed much more at risk, and we’ve seen this directly in subsequent outbreaks here.

“The work that we subsequently did on these risks ended up being crucial to the Government decision to pursue elimination.”

There’s a paradox at the heart of the rationalist project. The world is strange and complex, and we want to understand it, but we get closer to the truth by listening to others and doubting ourselves.

To presume we’ve ever found the truth is to lose it. We should try to be rational, but it’s irrational to convince ourselves we have succeeded.


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