The philosopher and polymath Michael Scriven has written extensively on the logic of explanations. Here are two of his most valuable pieces. The first one is how one can make good inferences from single cases studies and the second one one explanations in history.
1. Scriven, M. (1974). Maximizing the Power of Causal Investigations: The Modus Operandi Method. In W. J. Popham (Ed.), Evaluation in education: Current applications: 68-84: McCutchan Pub Corp. Download
2. Scriven, M. (1966). Causes, Connections, and Conditions in History. Philosophical Analysis and History. W. H. Dray, Harper & Row: 238-264. Download