We know that we don’t know: Children’s understanding of common ignorance in a coordination game

•Common ground is typically defined as what people know together (common knowledge).•It should also include what they do not know together (common ignorance).•We tested children’s ability to use four common knowledge/ignorance states.•4- to 8-year-olds played a novel coordination game with a partner.•The common ignorance states were more difficult than the common knowledge states. Common ground is the knowledge, beliefs, and suppositions shared between partners in an interaction. Previous research has focused extensively on what partners know they know together, that is, “common knowledge.” However, another important aspect of common ground is what partners know they do not know together, that is, “common ignorance.” A new coordination game was designed to investigate children’s use of common ignorance. Without communicating or seeing each other’s decisions, 4- to 8-year-olds needed to make the same decision as their partner about whether to try to retrieve a reward. To retrieve it, at least one of them needed to know a secret code. The knowledge/ignorance of both partners was ostensively manipulated by showing one partner, both partners, or neither partner the secret code in four conditions: common knowledge (both knew the code), common ignorance (neither partner knew the code), common privileged self knowledge (only children knew the code), and common privileged other knowledge (only their partner knew the code). Children’s decisions, latency, and uncertainty were coded. Results showed that the common ignorance states were generally more difficult than the common knowledge states. Unexpectedly, children at all ages had difficulty with coordinating when their partner knew the code but they themselves did not (common privileged other knowledge). This study shows that, along with common knowledge, common ignorance and common privileged self knowledge and other knowledge also play important roles in coordinating with others but may develop differently.