In four experiments, we tested the community-of-knowledge hypothesis, that people fail to distinguish their own knowledge from other people’s knowledge. In all the experiments, despite the absence of any actual explanatory information, people rated their own understanding of novel natural phenomena as higher when they were told that scientists understood the phenomena than when they were told that scientists did not yet understand them. In Experiment 2, we found that this occurs only when people have ostensible access to the scientists’ explanations; the effect does not occur when the explanations exist but are held in secret. In Experiment 3, we further ruled out two classes of alternative explanations (one appealing to task demands and the other proposing that judgments were mediated by inferences about a phenomenon’s understandability). In Experiment 4, we ruled out the possibility that the effect could be attributed to a pragmatic inference.