AbstractThe recognition heuristic (RH) claims that people base inferences on recognition only. This has been questioned by several studies which found that additional knowledge was influential. However, in some of these studies, participants' additional knowledge might have encompassed criterion knowledge thus rendering any inferential strategy superfluous. The present study was therefore designed to test the effect of criterion knowledge on use or non‐use of the RH. Eighty‐one participants made pair‐wise comparisons with respect to the size of Belgian cities and also provided estimates of the cities' actual size. We found that relative criterion knowledge (i.e., knowledge about the relative position of an object on the criterion dimension) did indeed play some role, but its exclusion left the main critical findings intact, nonetheless. We thus conclude that previous studies conducted in the paradigm of natural recognition should not be generally refuted by the argument of participants possessing criterion knowledge. Copyright © 2009 John Wiley & Sons, Ltd.