 There are different ways to do this. In the social sciences generally, the most popular approach takes a “diffusion” or “contagion” view of beliefs. A belief or idea is transmitted from individual to individual across their network connections, much like a virus can be transmitted (Rogers 1962). Imagine you live in a farming community where a new species of large caterpillar has started decimating crops. Suppose you come to believe that this kind of caterpillar is poisonous. You will immediately tell your friends and neighbors what you have learned, they will tell their friends and neighbors, and so on. Figure 1 shows this. Black nodes represent those “infected” with an idea. It starts with a focal individual and spreads, virally, through the community.