Historian Richard Pipes on Cause and Effect
"Causes, which are what the question "Why?" is meant to address, are the most difficult aspect of the historian's craft because they function on so many different levels. I have used the following analogy before, but because it is apt I will recall it to illustrate what I mean.
When you shake an apple tree and apples come cascading down, what "causes" them to fall? Is it the shaking of the tree? Is it the ripeness of the fruit which would have made them fall down, sooner or later, anyway? Or is it the law of gravity which makes objects fall downward to earth? In dealing with human events, we find similar levels of explanation, from the most specific to the most general, and it is next to impossible to ascertain which of them determines the outcome.
Usually, as in the case of the apple tree, one finds causes operating in tandem on three distinct levels: the longue duree, the intermediate span, and the short term - in the last of which accidents play a prominent role. The longue duree refers to trends over which neither individuals nor groups exert control; they are processes rather than events, and move glacially on their own. The decline of Rome, to cite one example, was an occurrence that no one could have prevented: decay was built into the system, and the rot progressed slowly until the system collapsed. Then, there are medium-term developments where individuals acting alone or in groups do make a difference: let me cite as an illustration the American Revolution and the constitutional arrangement that issued from it.
And, finally, there are accidents... My scholarly experience of nearly half a century, reinforced by a two-year stint in Washington, persuades me that it is entirely futile to seek any single explanation for major occurrences. Like a surgeon, the historian has to make skillful use of all kinds of instruments if he wishes to uncover the causes of non-specific events. Any one explanation is bound to be wrong. "
Source: Richard Pipes, Three "Whys" Of The Russian Revolution, 1st ed. (New York: Vintage Books, 1997). Page 9 - 10