Diffusion of innovations and contagion

A new religious feast, a new way of writing music, a freshly translated text -- all of these spread through a population the same way a disease does, or so this page's conjectures claim. The pattern has a name in two different fields: the Bass model in sociology and the contagion curve in epidemiology, both describing a slow start, a fast middle phase once enough people already have it, and a levelling-off once the practice has reached everyone it is going to reach. Applied here, that predicts a specific shape over time -- a visible take-off, and a gap between when a practice appears in one place and when it reaches the next that should shrink as contact between regions improves.

Monastic Bass diffusion tests the Bass model directly against how a monastic practice spread from house to house. The Sankore lag and The Arabic rate constant both look for a measurable time-lag along a specific route -- a West African trade network, an Arabic-region rate of change -- treating distance and contact as the thing that should predict the delay, more than the merit of the practice itself. Feasts travel at letter speed and The missal lags the chantry track how quickly a new religious feast or liturgical repertoire reached a new region, in one case as fast as ordinary letters travelled, in another lagging noticeably behind.