  Three influential papers on nonmonotonic logic appeared in 1980:  McDermott &amp; Doyle 1980,  Reiter 1980,  and  McCarthy 1980.  In each case, the formalisms presented in these papers were the result of a gestation period of several years or more. To set out the historical influences accurately, it would be necessary to interview the authors, and this  has not been done. However, there seem to have been two motivating factors: strategic considerations having to do with the long-range goals of AI, and much more specific, tactical considerations arising from the analysis of the reasoning systems that were being deployed in the 1970s.