Recent research has led to the development of interactive computer programs that enable a comprehensive search for reaction mechanisms. These programs enable a new strategy of interactive mechanistic study which borrows heavily from the century-old method of multiple working hypotheses proposed by T. C. Chamberlin. We propose that mechanistic studies should follow the method of considering at the outset a complete set of plausible mechanisms, rather than just one or a small number, which has the drawbacks described well by Chamberlin. This general methodology has become much more practical with the development of interactive computer programs that search comprehensively while building on the experimenter＇s prior knowledge. This paper illustrates the methods in detail, using as a vehicle the hydrogenation of ethylene, which is among the most studied reactions in the history of heterogeneous catalysis.