The central hypothesis of the limited enthusiasm model is that conversion growth in the church is driven by a sub-group of church members called enthusiasts. The enthusiasts are limited in their potential to convert as they cease to be enthusiasts after a given time. As such, church growth is limited as enthusiasts fail to reproduce themselves from a shrinking pool of potential converts. Thus, conversion falls below the loss of enthusiasts and church growth ceases with people left unconverted. The analogy is with the spread of a disease, where the enthusiasts are “infected” believers passing the faith on to unbelievers who catch the “disease” of religion.

System Dynamics Model

Unbelievers convert to believers through contact with enthusiasts who have “spread the faith” to them loops R and B1. Some new converts become enthusiasts, whereas some become inactive believers. Enthusiasts only remain active for a limited length of time before becoming inactive and taking no further part in spreading the faith, loop B2.

The dynamic hypotheses translate into the system dynamics model using three stocks and three feedback loops:

limited enthusiasm system dynamics model
Limited Enthusiasm Model

Growth is driven by the reinforcing loop R where enthusiasts are reproducing themselves through conversion. The feedback: more enthusiasts, more conversions, more enthusiasts, gives exponential growth. Growth is opposed by B1, which reduces conversions, thus slowing the exponential growth. When conversions have been reduced below the number who lose enthusiasm, B2, the number of enthusiasts starts to decline. Church growth slows and eventually halts.

For definitions and further detail see Assumptions and Parameters.

Spreading the Faith

For all aspects of spreading the faith, see:

Results of the Limited Enthusiasm Conversion Model

The results can only apply over short periods, up to about 15 years, as births and deaths are not included in the model. Thus the model is particularly suited to short, intense periods of growth, as is often seen during a revival.

The solution exhibits the typical steep rise in the growth of the church, eventually slowing down well short of the whole community being converted, see the graph below. Such growth only occurs if the reproduction potential exceeds a threshold of revival-type growth. This threshold depends on the proportion of unbelievers in society only. The enthusiasts rise and fall like the number of infected people in an epidemic, right axis. Growth ends because of a lack of enthusiasts.

Results of limited enthusiasm model

Thus, it is a combination of internal and external reasons that limit the church’s growth: The effectiveness of enthusiasts (internal); The size of the community (external).

Further Revival Results.