In a polarized political climate, with both sides of many issues claiming truth is on their side, it may be harder than ever to sift through and weigh evidence about issues in our everyday lives.

Professor Frederick Schauer of the University of Virginia School of Law offers insights about how to think about evidence in his new book “The Proof: Uses of Evidence in Law, Politics, and Everything Else,” published by Harvard University Press. He explores the use of evidence in courts but also in areas ranging from medicine to art to history and beyond, and explains what kinds of evidence matter in different contexts.

“This book is a way to help people ask about evidence and answer questions about whether things in the world of fact are actually true or not,” he said. “There’s more information out there, and because there is more information out there, more of it is wrong. Especially in the internet era, there are fewer informational filters out there. And it’s easier to just say stuff and more people, to their credit, are trying to say, ‘Is there evidence for that?’”

Schauer, a preeminent constitutional law scholar and legal theorist who has taught evidence for more than 40 years, had long planned on writing a book on the topic, but was spurred to finally get started following the 2020 presidential election and the events of Jan. 6, 2021, “which put questions of evidence on the front page of the newspapers every day and in the front of everyone’s consciousness.”

“Just as they say that ‘If you have a hammer, every problem looks like a nail,’ I became increasingly aware of the issues of evidence and proof in almost everything I saw, did or read about,” Schauer said. “And most of this was not about law with a capital ‘L,’ but about public policy, politics, science, art, sports and pretty much everything I was interested in.”

As a framework for examining the issues at stake, Schauer relies on probabilistic thinking and analysis.

“One of the implications of thinking probabilistically is that what might appear as weak evidence is still evidence, and might be good enough depending on the context and the consequences,” he said. “We properly require proof beyond a reasonable doubt to convict someone of a crime, but how much evidence does a physician need to recommend an experimental drug for patients with afflictions for which there is no other remedy? How much evidence was necessary for historians to conclude that Thomas Jefferson was the father of the children of Sally Hemings?”

Most of the conclusions we draw from evidence are probabilities, Schauer claims in the book.

“One lesson is probabilities matter, and we should think about evidence in terms of probabilities and likelihoods, even in nonmathematical ways,” he said. “And the lesson that goes from that is that very often weak evidence is good enough, better evidence is better than worse evidence, but sometimes weak evidence is good enough.”

It’s a bigger problem to be too skeptical of evidence, which could lead to not relying on evidence at all.

Until recently, he said, people were more skeptical than they should have been about women’s claims of sexual assault, for example in the case of allegations against former movie producer Harvey Weinstein or former President Bill Clinton. He noted that these are cases where a little evidence — from many sources — can go a long way.

“It may turn out that multiple accusations, each of which only have some evidence, but not a whole lot of evidence, all together lead us to believe someone did at least something or at least one thing,” he said. “None of the accusations against Bill Clinton are beyond the shadow of a doubt. True. But when you add them all up, did Bill Clinton do at least one of these things? Yes.”

He also explores paradoxes in how courts handle evidence. Traditionally, courts have not allowed polygraphs as evidence, with the exception of New Mexico’s state courts, which have permitted them since 1983.

“Some of that skepticism is justified, but it turns out that if we don’t use [such evidence] at all, what happens very often in court is we allow juries to decide whether someone is lying or telling the truth. And even if lie detection evidence — including modern, neuroscientific, MRI lie detection evidence — might get it wrong 10 to 15% of the time, juries trying to figure out who’s lying and telling the truth get it wrong 50% of the time, or close to 50% of the time.

“So should we rely on imperfect polygraphs or neuroscience, as opposed to a lot more imperfect juries relying on folk wisdom and a whole bunch of other things? I think, yes.”

In his book, Schauer also discusses the movement for evidence-based medicine, which is based on the idea that the gold standard for medical diagnosis and treatment is placebo-controlled experiments.

“But it turns out that that’s not always possible,” he said. “And a lot of practicing physicians — very experienced and very talented ones — base their diagnoses and base their treatments on long experience — that’s evidence too.”

Schauer is a David and Mary Harrison Distinguished Professor of Law at UVA. His other books include “Playing By the Rules: A Philosophical Examination of Rule-Based Decision-Making in Law and in Life,” “Free Speech: A Philosophical Enquiry,” “Thinking Like a Lawyer: A New Introduction to Legal Reasoning” and “The Force of Law.” He is a fellow of the American Academy of Arts and Sciences and a corresponding fellow of the British Academy.

Founded in 1819, the University of Virginia School of Law is the second-oldest continuously operating law school in the nation. Consistently ranked among the top law schools, Virginia is a world-renowned training ground for distinguished lawyers and public servants, instilling in them a commitment to leadership, integrity and community service.

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