Andrea Bender
, respectively). The presence and numerical value of a base in such systems have implications on several levels: They shape the system structure in creating higher (counting) units; they affect how users cognitively represent and process numerical information; and they play a role in establishing cultural conventions for standardizing systems, setting thresholds or converting between scales. This paper investigates how each of these levels is implicated when numeration systems with diverging bases are used in parallel, from small-scale traditional contexts to daily-life situations and high-stakes domains in a globalized world. In focusing on the challenges that parallel systems were designed to tackle, as well as the challenges they cause, the paper highlights bases as both a result and a tool of cultural evolution.This article is part of the theme issue 'A solid base for scaling up: the structure of numeration systems'.