Ideas and products and messages and behaviors spread just like viruses do.

Is there a simple rule of thumb that distinguishes a group with real social authority from a group with little power at all? As it turns out, there is. It’s called the Rule of 150,

Six degrees of separation doesn’t mean that everyone is linked to everyone else in just six steps. It means that a very small number of people are linked to everyone else in a few steps, and the rest of us are linked to the world through those special few.

In a social epidemic, Mavens are data banks. They provide the message. Connectors are social glue: they spread it. But there is also a select group of people—Salesmen—with the skills to persuade us when we are unconvinced of what we are hearing, and they are as critical to the tipping of word-of-mouth epidemics as the other two groups.

But we need to remember that small changes in context can be just as important in tipping epidemics, even though that fact appears to violate some of our most deeply held assumptions about human nature.

When people are in a group, in other words, responsibility for acting is diffused.

in our minds, a very specific, biological

Perhaps the most sophisticated analysis of this process of translation comes from the study of rumors, which are—obviously—the most contagious of all social messages. In his book The Psychology of Rumor, the sociologist Gordon Allport writes of a rumor involving a Chinese teacher who was traveling through Maine on vacation in the summer of 1945,

“The Magical Number Seven.” This is the reason that telephone numbers have seven digits. “Bell wanted a number to be as long as possible so they could have as large a capacity as possible, but not so long that people couldn’t remember it,” says Jonathan Cohen, a memory researcher at Princeton University. At eight or nine digits, the local telephone