Research Findings

Infectious Ideas: Why do Radical Innovations Take Root?


March 18, 2021

Living in the midst of a pandemic, we have all become familiar with the idea of contagion. An epidemic spreads through exposure to an infectious agent, like a novel virus. In a basic contagion model, the spread of a disease is a function of contact with the agent and its degree of infectiousness. Epidemiologists often model the risk of contagion as a function of contact (or frequency or level of contact) with the infected and the agent’s virulence.

When it comes to triggering radical institutional change, do ideas work the same way?

In a recent article, a team of sociologists and economists to which I belong posed this question in trying to account for why the Protestant Reformation spread so rapidly after Luther’s rebellion against the Catholic Church began in 1517. The Protestant Reformation was one of the most transformative periods in modern European (if not world) history. Martin Luther, a previously obscure theology professor at a provincial university, triggered it. That much is well known.

However, how did Luther’s movement succeed? Why did it do what previous reform movements failed to do? How did it break out of its provincial stronghold to be widely adopted across Europe?

This is an especially important question because Luther’s ideas attacked the religious, political, and cultural status quo. They faced fierce opposition from the defenders of Catholic orthodoxy and the Church’s effective religious monopoly. Previous challenges like Luther’s had been either contained or ruthlessly crushed. Luther’s reforms began to be widely instituted by cities across the German-speaking world within about a decade.

In sociology, “social diffusion” refers to the outward movement of an innovation (like Protestantism in the 16th Century) from one source to another. Generally, diffusion research offers three families of mechanisms to account for the adoption of radical innovations like Protestantism: learning, contagion, and social influence.

Previous research has never attempted to test all three mechanisms in explaining institutional changes. Our study took on the challenge. By combining data on Luther’s extensive publishing activity (learning), social exposure to Protestantism through trade route proximity to “infected” towns (contagion), and Luther’s personal network ties to people in these cities (social influence, exercised through letters, visits and Wittenberg students), we were able to model how multiple diffusion processes might be at work.

Breaking with existing literature on the Reformation that put all the emphasis on how printing led to the spread of Protestantism, drawing from the various types of mechanisms identified in the diffusion literature, we developed a theory that combines social influence (via Luther’s social network ties), which we refer to as relational diffusion, with contagion (via trade routes), which we call spatial diffusion.

We show that Luther’s influence network alone does not explain the early success of the Reformation, but his network in combination with the pre-existing ties created by trade routes explains much of its success.

Surprisingly, given the wealth of writing crediting the printing press with making possible Protestantism, we find that printing did not contribute to the early Protestant breakthrough compared with contact with neighboring Protestant towns and Luther’s efforts to spur reform through personal appeals. Printing did matter later on, as time wore on and more and more powerful rulers adopted it after 1530.

Explaining the success of the Reformation

Traditional historians of the Reformation place great emphasis on the unique role played by Martin Luther. In this telling, Luther was a personality of monumental historical importance. He was a tireless proponent of the Reformation through his preaching, writing, correspondence, recruitment of students at Wittenberg’s university, and careful cultivation of ties to political elites.

Nevertheless, how do we know that Luther was actually a key figure net of the many factors that could have influenced why cities adopted reform? Could the Reformation as a movement have taken off without him?

We focused on Martin Luther’s role in spreading the early Reformation (pre-1530). We reconstructed his influence network to examine whether his local connections increased the odds of adopting Protestantism. We conceived of the process as leader-to-follower, originating with Luther and flowing to local elites through personal ties. Luther had ties with local elites in towns across Central Europe, who, in turn, exerted influence in their towns. Put simply, our argument is that social influence flowed from an opinion leader through social ties to cities that were potential adopters.

At the same time, we recognized that Luther’s influence would not have been the only factor that influenced adoption, and other social processes were operating. Our argument is that personal/relational diffusion via Luther’s ties combined with spatial/structural diffusion via trade routes to help Protestantism make a breakthrough from a regional reform movement to a general rebellion against the Roman Catholic Church.

Figure 1 illustrates this idea. It depicts Luther as an opinion leader who mobilized his personal network as an ensemble of letters, visits, and student relationships, and also how Luther’s network blends with the spatial network to create complex contagion processes operating at the intersection of information flow and social influence.

We argued that Luther’s influence networks and spatial diffusion are complementary mechanisms. Luther’s influence spread outward from Wittenberg across the region of Saxony, but it also “infected” distant places across Central Europe through his ties to influential people. Our model of social influence is consistent with a complementary process whereby Luther converted cities that did not adjoin Wittenberg through direct social influence, which, in turn, further spread the Reformation by seeding clusters of adoption that could trigger subsequent diffusion. This would have quickly accelerated the viral spread of Protestantism.

We used network simulations to test whether either Luther’s personal network alone, or spatial diffusion alone can explain the adoption of the Reformation by 1530.

Our results in Figure 2 show that diffusion of the early Reformation appears to have been a combined process of two mechanisms. First, Luther infected a certain proportion of the cities in which he had influence, often far from Wittenberg, which then adopted the Reformation. Because of their spatial relation to uninfected cities, these adopted cities created local social reinforcement that persuaded further cities to adopt, even if they were not directly under Luther’s influence.

Moreover, Luther’s personal influence affected cities that were connected to one another, creating the “infected” clusters that furthered diffusion across space. The result was a pandemic that raised the number of adopted cities as the interaction of multiplex networks (trade routes and Luther) via multiple diffusion processes jointly facilitated the spread of the early Reformation.

Although we apply our theory to the Reformation, we believe it has implications further afield. Our approach is potentially useful for the study of diffusion of other social and political movements around the world, past and present. As we have become painfully aware in recent months, viral forces can result in massive social changes both immediately and in the longer range.

Read more

Sascha O. Becker, Yuan Hsiao, Steven Pfaff, and Jared Rubin. “Multiplex Network Ties and the Spatial Diffusion of Radical Innovations: Martin Luther’s Leadership in the Early Reformation” in American Sociological Review 2020.

Image: jean louis mazieres via Flickr (CC BY-NC-SA 2.0)

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