How do we know what we know, and how does this knowledge drive further learning? Perfors combines empirical work with computational and mathematical modelling to investigate how data in the world, along with people's assumptions about it, shape and are shaped by cognition. Perfors argues that because humans are social creatures, understanding cognition requires understanding the social assumptions we make about the origin of the data we see; this is evident in areas from concept learning to language to decision making to information search.