A common type of second-hand evidence is historical information—verifiable facts that a writer knows from research. This kind of evidence can provide background and context to current debates; it also can help establish the writer’s ethos because it shows that he or she has taken the time and effort to research the matter and become informed. One possible pitfall is that historical events are complicated. You’ll want to keep your description of the events brief, but be sure not to misrepresent the events. In the following paragraph from Hate Speech: The History of an American Controversy (1994), author Samuel Walker provides historical information to establish the “intolerance” of the 1920s era.
The 1920s are remembered as a decade of intolerance. Bigotry was as much a symbol of the period as Prohibition, flappers, the stock market boom, and Calvin Coolidge. It was the only time when the Ku Klux Klan paraded en masse through the nation’s capital. In 1921 Congress restricted immigration for the first time in American history, drastically reducing the influx of Catholics and Jews from southern and eastern Europe, and the nation’s leading universities adopted admission quotas to restrict the number of Jewish students. The Sacco and Vanzetti case, in which two Italian American anarchists were executed for robbery and murder in a highly questionable prosecution, has always been one of the symbols of the anti-immigrant tenor of the period.
(1994)
To support the claim that the 1920s was a period characterized by bigotry, Walker cites a series of historical examples: the KKK, immigration laws, restriction targeting certain ethnicities, and a high-profile court case.
Historical information is often used to develop a point of comparison or contrast to a more contemporary situation. In the following paragraph from Charles Krauthammer’s op-ed “The 9/11 ‘Overreaction’? Nonsense,” the political commentator does exactly that by comparing the War on Terror to previous military campaigns in U.S. history.
True, in both [the Iraq and Afghanistan] wars there was much trial, error, and tragic loss. In Afghanistan, too much emphasis on nation-building. In Iraq, the bloody middle years before we found our general and our strategy. But cannot the same be said of, for example, the Civil War, the terrible years before Lincoln found his general? Or the Pacific campaign of World War II, with its myriad miscalculations, its often questionable island-hopping, that cost infinitely more American lives?
(2011)
Notice that Krauthammer’s historical evidence is brief but detailed enough to both show his grasp of the history and explicitly lay out his comparison. Simply saying, “These wars are no different from the Civil War or World War II” would have been far too vague and thus ineffective.
The name of the post hoc ergo propter hoc fallacy is Latin for “after which therefore because of which.” What that means is that it is incorrect to claim that something is a cause just because it happened earlier. In other words, correlation does not imply causation.
| example | We elected Johnson as president and look where it got us: hurricanes, floods, stock market crashes. |
That’s a simple example, but in reality causality is very tricky to prove because few things have only one cause. When using historical evidence, you should be especially aware of this fallacy. Check your facts. Consider the complexity of the situation. Proceed with caution.