Some theories of reasoned assumptions : an essay in rational psychology

We examine several formulations of the common practice of jumping to conclusions when actions demand decisions but solid knowledge fails. This practice permeates artificial intelligence, where systems assume many conclusions automatically as defaults simply because the questions they decide are known to occur frequently, and where other assumptions are formulated and adopted only when ignorance stalls action. After developing the motivations and general nature of these inferences, we introduce a formal basis for describing them. This formulation allows separate introduction of the several ideas involved, and so facilitates characterization of some important combinations and some previous proposals. Initial results are proved about these theories, including the aptness of the formal notions with respect to the intuitive motivations. Benefits of this formulation include an indication of the ways notions from logic and metamathematics can enter into psychologies without subscribing to all of logic or metamathematics, an indication of the importance of conservation of mental states in the description of psychologies, and formal and intuitive relations between the approach of reasoned assumptions and its popular alternatives, deductivism and Bayesianism.