Judgments which assign relative importance to the causes of particular results can be objective. Historians usually do and can use a factual principle of selection to distinguish between causes and conditions and between more and less important causes. The judgments which distinguish between causes and conditions and the judgments which distinguish between more and less important causes require radically different analyses. In A. M. Jones's work on the decline and fall of Rome, he argued that increased barbarian pressure on the (...) West was the most important cause of Rome's fall. It is possible to understand this statement as an instantiation of the following: A was a more important cause of P relative to 0 than was B if 1) A and B were each a cause of P relative to 0 and 2) either A was necessary for P or B was not necessary for P and 3) had B not occurred, something would have occurred which more closely approximates P than had A not occurred. (shrink)