Full Idea
Objects or events in the world must really stand in some appropriate 'structural' relation before explanation is possible.
Gist of Idea
An explanation needs the world to have an appropriate structure
Source
David-Hillel Ruben (Explaining Explanation [1990], Ch 7)
Book Reference
Ruben,David-Hillel: 'Explaining Explanation' [Routledge 1990], p.210
A Reaction
An important point. These days people talk of 'dependence relations'. Some sort of structure to reality (mainly imposed by the direction of time and causation, I would have thought) is a prerequisite of finding a direction to explanation.