To infinity and beyond: Children generalize the successor function to all possible numbers years after learning to count
Recent accounts of number word learning posit that when children learn toaccurately count sets (i.e., become "cardinal principle" or "CP" knowers),they have a conceptual insight about how the count list implements thesuccessor function - i.e., that every natural number *n *has a successordefined as *n+1* (Carey, 2004, 2009; Sarnecka & Carey, 2008). However,recent studies suggest that knowledge of the successor function emergessometime after children learn to accurately count, though it remainsunknown when this occurs, and what causes this developmental transition. Wetested knowledge of the successor function in 100 children aged 4 through 7and asked how age and counting ability are related to: (1) children'sability to infer the successors of all numbers in their count list, and (2)knowledge that *all *numbers have a successor. We found that children donot acquire these two facets of the successor function until they are about5.5 or 6 years of age - roughly 2 years after they learn to accuratelycount sets and become CP-knowers. These findings show that acquisition ofthe successor function is highly protracted, providing the strongestevidence yet that it cannot drive the cardinal principle induction. Wesuggest that counting experience, as well as knowledge of recursivecounting structures, may instead drive the learning of the successorfunction.