James Steiner-Dillon: Why can’t Americans agree on, well, nearly anything? Philosophy has some answers.

Does wearing a mask stop the spread of covid-19? Is climate change driven primarily by human-made emissions? With these kinds of issues dividing the public, it sometimes feels as if Americans are losing our ability to agree about basic facts of the world. There have been widespread disagreements about matters of seemingly objective fact in the past, yet the number of recent examples can make it feel as though our shared sense of reality is shrinking.

As a law professor, I’ve written about legal challenges to vaccination requirements and covid-19 restrictions, as well as what counts as “truth” in court. In other words, I spend a lot of time mulling over how people define truth, and why U.S. society has such a hard time agreeing on it these days.

There are two ideas that can help us think about polarization on matters of fact. The first, “epistemic pluralism,” helps describe U.S. society today, and how we got here. The second, “epistemic dependence,” can help us reflect on where our knowledge comes from in the first place.

I define epistemic pluralism as a persistent state of public disagreement about empirical facts.

When it comes to things that can be proved or disproved, it’s easy to think that everyone could come to the same factual conclusions, if only they had equal access to the same information — which, after all, is more freely available today than at any point in human history. But, while the inequality of access to information plays a role, it is not so simple: Psychological, social and political factors also contribute to epistemic pluralism.

In a society characterized by freedom of conscience and freedom of expression, individuals bear “burdens of judgment,” as the American philosopher John Rawls wrote. Without the government or an official church telling people what to think, we all have to decide for ourselves — and that inevitably leads to a diversity of moral viewpoints.

This intellectual freedom contributes to epistemic pluralism. So do factors such as educational inequalities, the proliferation of information from untrustworthy sources online and misinformation campaigns. All together, they provide ample opportunity for people’s shared sense of reality to fragment.

Another contributor to epistemic pluralism is just how specialized human knowledge has become. No one person could hope to acquire the sum total of all knowledge in a single lifetime. This brings us to the second relevant concept: epistemic dependence.

Knowledge is almost never acquired firsthand, but transmitted by some trusted source. To take a simple example, how do you know who the first president of the United States was? No one alive today witnessed the first presidential inauguration. You could go to the National Archives and ask to see records, but hardly anyone does that. Instead, Americans learned from an elementary school teacher that George Washington was the first president, and we accept that fact because of the teacher’s epistemic authority.

There’s nothing wrong with this; everyone gets most knowledge that way. There’s simply too much knowledge for anyone to verify independently all the facts on which we routinely rely.

However, this raises a tricky problem: Who has sufficient epistemic authority to qualify as an expert on a particular topic? Much of the erosion of our shared reality in recent years seems to be driven by disagreement about whom to believe.

Whom should a nonexpert believe about whether a covid-19 vaccine is safe and effective? Whom should a Georgia voter believe about the legitimacy of their state’s results in the 2020 election: Sidney Powell, an attorney who helped Donald Trump’s legal team try to overturn the 2020 election, or Georgia Secretary of State Brad Raffensperger?

The problem in these and other cases is that most people are unable to determine the truth of these matters on their own, yet they are also unable to agree on which experts to trust.

There isn’t a simple solution to this problem. But there may be rays of hope.

Intelligence alone doesn’t decrease people’s tendency to let their group identities sway their view of facts, according to Kahan and his colleagues — but very curious people tend to be more resistant to its effects.

There are many forces pulling our collective understandings of the world apart; with some effort, however, we can try to reestablish our common ground.