HISTORICAL parallels must not be overdrawn. From the simple fact that Napoleon started for Moscow in June 1812 and got there by September and that Hitler started for the same place in June 1941 and did not get there by September almost nothing of any use to us today can be inferred. Such a comparison is essentially between incomparables. But because much loose prophecy is heard, based on crude analogies between the Napoleonic period and our own day, it by no means follows that we can learn nothing by a cautious comparison between the broad aspects of the two periods.
This is not the place to go into the elaborately philosophical implications of the problem of historical uniformities. It should be sufficient to point out that from the point of view of common sense the notion that historical events are wholly unique is simply not tenable. In medical practice, for instance, no case, even of a relatively simple disease like pneumonia, is exactly like any other case; each patient presents to the physician a problem in some way unique. But not wholly unique, or the medical profession could never have achieved the triumphs it undoubtedly has achieved. The physician expects to learn from experience -- that is, from history. The fact is that most "practical" men -- farmers, sailors, engineers -- habitually act on what it is no mere quibble to call a study of historical uniformities. They may make mistakes. If they act as if their experience gave them absolute uniformities,