What makes one event have more historical importance than another event? Why, for example, do historians consider Caesar's decision to cross the Rubicon more important than Caesar's decision to shave in the morning? In this example, the answer should be obvious. The contrast is between a decision of great consequence and a decision of little consequence. Perhaps we can generalize from the example to say that the ranking of events with respect to their historical importance is a function of the magnitude of their respective consequences.
W. H. Dray holds that in some cases historical importance is determined by factors other than the size of consequences. For example, events may be important because of what they anticipate or what they reveal.