Decomposing modal thought

Cognitive scientists have become increasingly interested in understanding how natural minds represent and reason about possible ways the world could be. However, there is currently little agreement on how to understand this remarkable capacity for modal thought. We argue that the capacity for modal thought is built from a set of relatively simple component parts, centrally involving an ability to consider possible extensions of a part of the actual world. Natural minds can productively combine this ability with a range of other capacities, eventually allowing for the observed suite of increasingly more sophisticated ways of modal reasoning. We demonstrate how our (de)compositional account is supported by both the trajectory of children’s developing capacity for reasoning about possible ways the world could be and by what we know about how such modal thought is expressed within and across natural languages. Our approach makes new predictions about which kinds of capacities are required by which kinds of experimental tasks and, as a result, contributes to settling currently open theoretical questions about the development of modal thought and the acquisition of modal vocabulary in children. Our work also provides a more systematic way of understanding possible variation in modal thought and talk, and, more generally, paves the way towards a unified theory that will ultimately allow researchers across disciplines to relate their findings to each other within a framework of shared assumptions.