Unspoken Rules: Resolving Underdetermination With Closure Principles

When people learn normative systems, they do so based on limited evidence. Many of the possible actions that are available to an agent have never been explicitly permitted or prohibited. But people will often need to figure out whether those unspecified actions are permitted or prohibited. How does a learner resolve this incompleteness? The learner might assume if an action-type is not expressly forbidden, then acts of that type are permitted. This closure principle is one of Liberty. Alternatively, the learner might assume that if an action-type is not expressly permitted, then acts of that type are prohibited. This closure principle would be one of Residual Prohibition (Mikhail, 2011). On the basis of principles of pedagogical sampling (e.g., Shafto, Goodman, & Griffiths, ), we predicted that participants would infer the Liberty Principle (LP) when trained on prohibitions, and they would infer the Residual Prohibition Principle when trained on permissions. This is exactly what we found across several experiments. We also found a bias in favor of Liberty insofar as participants trained on both a prohibition and a permission rule tended still to infer the LP. However, we also found that if an action is potentially harmful, this diminishes the tendency to infer the LP.