Reasoning, problem solving, indeed the general process of acquiring knowledge, is not an isolated, homogenous affair involving a one agent using a single form of representation, but more typically a complicated, collaborative, heterogeneous activity. This paper describes an effort to expand our understanding of such reasoning and to develop tools to enable individuals and groups to use computers more effectively in practical problem-solving tasks. Natural deduction and problem solving A recent article in the New York Times reported the discovery of mass in the neutrino by a team of 120 scientists from 23 research institutions. The discovery involved the design and construction of a massive experiment involving a tank inside a deep zinc mine, filled with 12.5 million gallons of water, and equipped with specially designed light amplifiers covering the inside of the tank. Using this set-up as a neutrino detector to compare “flavors” of neutrinos coming directly from the atmosphere ve...