Abstract The suppression of optional variability is a cornerstone of English prescriptivism. For Dutch, however, it is unknown whether this concept is equally important. The goal of this paper is to investigate which stance towards variation is taken in Dutch prescriptivism, and what arguments are used to support this stance. I address these questions by looking at 236 usage advice items from 73 Dutch prescriptive publications concerning the comparative particles als and dan . This data shows a clear division in the allowance of variation. With the standard comparative (groter als/dan ), variation is often allowed, but with equative constructions ( even groot als ) only one form is ever accepted. Furthermore, the allowance of variation decreases over time. The argumentation that is used shows few patterns, and is frequently completely absent. This indicates the existence of an ipse dixit (‘assertion without proof’) tradition in Dutch prescriptivism since 1900.