When they are small, movements tend to experience very rapid growth. They might double in size multiple times in a given year. Over time, as movements get larger, this growth tends to plateau. Why? Is it because, as time passes, evangelists get less enthusiastic? The case studies of movements I have collected don’t suggest this is the case. There’s a simpler and, I think, inevitable cause that actually hallmarks a success, not a failure.

When people hear this fact, they often ask: how are they counted? One implication of this question is, are they counted in a way that others can accept as credible? As a basis for an answer, let’s begin with a broader question: how do Christian denominations, in general, count their members? How, for example, do denominations in America count?