How do people use human-made objects (artifacts) to learn
about the people and actions that created them? We test the
richness of people’s reasoning in this domain, focusing on the
task of judging whether social transmission has occurred (i.e.
whether one person copied another). We develop a formal
model of this reasoning process as a form of rational inverse
planning, which predicts that rather than solely focusing on
artifacts’ similarity to judge whether copying occurred, people
should also take into account availability constraints (the
materials available), and functional constraints (which
materials work). Using an artifact-building task where two
characters build tools to solve a puzzle box, we find that this
inverse planning model predicts trial-by-trial judgments,
whereas simpler models that do not consider availability or
functional constraints do not. This suggests people use a
process like inverse planning to make flexible inferences from
artifacts’ features about the source of design ideas.