Conspiracy theories have been around for hundreds of years, but with the rise of the internet, the speed with which they spread has accelerated and their power has grown. Back in the 1950s, Joseph McCarthy promoted conspiracy theories that communists had deeply infiltrated and threatened all branches and agencies of the U.S. government; last month, Donald Trump retweeted conspiracy theories in the wake of Jeffrey Epstein’s death.

Conspiracy theories are all around us. But how do they work, who believes them, and why? What kind of damage can they do—and how can we do a better job of controlling that damage, as individuals and as a society?

The answers are complicated—but with misinformation proliferating and mutating like a virus, and the health of civil society and democratic governance at stake, it’s crucial to try to address them and contain them, according to Kelly M. Greenhill, a professor of political science and director of the Tufts International Relations Program.

Greenhill—who teaches the senior seminar course Better than the Truth: Extra-factual Information in International Politics, and is revising for publication a book on the influence of conspiracy theories and other forms of unverified (or “extra-factual”) information on international politics—shared thoughts and theories about conspiracy theories in a recent conversation with Tufts Now.

Tufts Now: What exactly is a conspiracy theory?

Kelly M. Greenhill: The term means different things to different people. For some, conspiracy theory is employed as a catchall term to describe a broad array of generally outlandish and almost invariably false alleged clandestine plots that are usually—but not always—devised by rich, powerful actors and/or governments to dupe and/or exploit others. A wide range of wacky and eye roll inducing conspiratorial claims certainly do exist. But to describe all conspiracy theories with such a broad brush is both analytically misleading and politically unhelpful.

More specifically, the term conspiracy theory simply refers to a hypothesized—as opposed to verified and proven—conspiracy. So what then is a conspiracy? Paraphrasing the Oxford English Dictionary, a conspiracy is a secret plot or agreement between two or more parties for an illegal or dishonest purpose. Again, many conspiracy theories are false, crazy, and sometimes even dangerous, but other such theories are eventually revealed to be true, after which they are referred to as conspiracies—or simply crimes—rather than conspiracy theories.

One famous example is the Watergate conspiracy theory. After first being dismissed and ridiculed by the Nixon Administration and its political supporters, this theory was eventually revealed by Washington Post reporters Bob Woodward and Carl Bernstein to be a genuine conspiracy, concocted by its plotters to dig up dirt on Democrats and tip the scales in favor of Nixon’s reelection.

How do conspiracy theories arise and take hold?

In terms of their origins, conspiracy theories often emerge in the wake of surprising and unsettling events, such as terrorist attacks, mass shootings, plane crashes, economic shocks, and the deaths of famous or important individuals. In the face of tragedy, danger, and confusion, people look for answers, for ways to process and impose a sense of order on frightening and seemingly inexplicable occurrences.

Conspiracy theories, like rumors and other forms of what I call extra-factual information—or EFI—are then adopted and treated as possible or actual truth because they can serve as a kind of improvised news, filling in holes in people’s knowledge and providing psychic relief. Even if untrue, EFI can help individuals cope with fear and uncertainty by generating shared explanations that offer clarity, address anxieties, and provide rationalizations for otherwise incomprehensible events.

Conspiracy theories—like EFI, more generally—can turn politically problematic and even dangerous when politicians and other actors seek to stoke and exploit belief in unverified information for political gain. Such uses run the gamut from the pedestrian—such as using EFI to gain votes or support for particular public policies or programs—to the deadly, such as using EFI to mobilize segments of a population to do harm to other segments of that population. In the most extreme cases, this can result in genocide, as happened, for instance, in Nazi Germany and in Rwanda in 1994.

Is there anything different about conspiracy theories today—how they work and how they are used—compared to in the past?

The internet certainly offers a new and very powerful platform—in terms of speed and scale—for the spread of conspiracy theories as well as other forms of EFI. Moreover, the current political moment is unusual in terms of the unbridled willingness of some incumbent leaders and media outlets that support them to spread unverified and, in some cases, even demonstrably false conspiracy theories as alleged truth. It is no accident that the current U.S. president became known as the “conspiracy candidate” during the 2016 election, as Donald Trump has been a particularly prolific purveyor of a wide array of conspiracy theories, many of which are of the peculiar and potentially perilous variety.

In addition, in the current political moment, there are a number of non-state actors, many operating in fringe media outlets, who traffic in conspiracy theories, usually of this same outlandish and political smear-focused variety. That politicians and other actors are spreading large numbers of these fictive narratives, apparently for personal and financial gain, is troubling and potentially corrosive to democratic governance.

At the same time, the deployment of conspiracy theories as political tools is nothing new—their prevalence in mainstream political discourse has ebbed and flowed over time. For instance, opposition politicians in late nineteenth century Britain told tales of a German conspiracy to invade and occupy the British Isles to try to build support for conscription and increased defense spending.

In the aftermath of World War I, U.S. officials warned of a dangerous plot by Bolsheviks and anarchists to overthrow the government in an effort to justify mass deportations, limit “undesirable” immigration, and to build support for a variety of other extra-legal activities aimed at crushing organized labor movements.

In the 1930s and 1940s, the Nazis spread noxious narratives about an alleged Jewish conspiracy to take over the world to justify and build support for military expansion and the persecution and later killing of Jews. As I describe in my forthcoming book, Fear and Present Danger: Extra-factual Sources of Threat Conception and Proliferation, while the details of each of these historical instances are distinct, the number of cases in which conspiracy theories are deployed as political tools is long, and their effects are often quite consequential and enduring.

How do politicians use conspiracy theories to manipulate public thinking, and in what situations? How much does this happen?

As possessors of the bully pulpit, political elites can push conspiracy narratives—as well as other forms of EFI—into mainstream political discourse. Decisions to do so are almost invariably politically motivated, whether with personal or partisan interest in mind. This is true on both sides of the political spectrum. Although in recent decades we’ve witnessed a disproportionate share of this kind of behavior on the right—and, most especially, and increasingly dangerously, on the far-right—side of the political spectrum.

Of course, some drivers and sources of conspiracy theorizing transcend political viewpoints. One example is the recent death by hanging of convicted sex trafficker Jeffrey Epstein while in custody in a New York jail. The nature and content of the conspiracy theories surrounding Epstein’s death differ radically depending on the source, and that source’s potential motivation for spreading his/her/their theory.

Even so, dozens of conspiracy theories about Epstein’s demise have arisen because of the suspicious circumstances surrounding his untimely death, the heinous nature of his crimes—both established and alleged—and his connections to scores of rich and powerful people who could have been directly implicated had Epstein lived to testify in open court. Some of the theories floating around will sound outlandish and wacky to most audiences, others strikingly plausible to more than a few.

What concrete effects do conspiracy theories have on people’s actions, and on decision-making and policymaking?

In the short term, this kind of psychological manipulation only works when the audience in question already believes or is open to persuasion to what the politician is selling. Like any form of EFI, exposure to a new conspiracy theory can have one of three effects on an individual: it can cause that person to believe something new; it can bolster the individual’s existing beliefs, either in line with the conspiracy theory or in opposition to it; or it can have no effect on the individual’s attitudes or beliefs.

Over the longer term, however, the picture is a bit less clear. Laboratory experiments suggest, for instance, that exposure to conspiracy theories in which the government is the culprit leads to a lower likelihood of voting in future elections and decreased willingness to proactively engage on issues related to their workplaces, climate change, and vaccinations. While further study is needed, such studies highlight reasons for concern about the future health of civil society, trust in institutions, and the health of democratic governance in countries where politicians regularly traffic in conspiracy theories.

What can be done to combat the influence of conspiracy theories in our government and in our own decision-making?

Research has shown that it is far easier to change people’s behavior than to change their underlying beliefs. So the most expedient and effective strategy would be to incentive those who traffic in conspiracies for political gain to change their behavior, irrespective of their beliefs. How does one do this? As we enter another consequential national election cycle, concerned members of the public should make clear to incumbents and candidates alike that they expect their leaders to deal in facts rather than to traffic in speculation, and that a failure to take heed will translate into votes for alternatives who eschew conspiratorial rhetoric and fear-mongering.

Those opposed to media outlets and social media platforms that engage in and/or permit the same sorts of corrosive behaviors should vote with their feet, change the channel, literally and metaphorically, and, when possible, send strong and direct signals to advertisers that they prefer media channels that focus on rooting out facts rather than trading in easily debunkable and politically-motivated conspiracies.

My research has shown that prior exposure to EFI makes individuals between two and eight times more susceptible to accepting it as definitely or plausibly true. Dissuading actors from introducing and/or disseminating conspiracy theories and other forms of politically motivated EFI is therefore a critical way to protect both our democracy and our own decision-making from potential influence and manipulation.

Monica Jimenez can be reached at monica.jimenez@tufts.edu.