Evaluating Historical Sources

By James R. Giese
Published on 10/07/2008

The historical record is highly selective, often biased, and always incomplete. Most of what happened in the past is undocumented, and not every document produced is preserved for future use. Much of what is available has been accumulated by accident. Furthermore, much historical evidence is actually incidental to the situations described. On the other hand, some of the available records are left because of the self-conscious action of historical actors. Many people keep journals and write diaries, autobiographies, and business and personal letters, some of which are written explicitly for posterity and the historical record.

Some primary sources are more useful than others, depending, of course, on what question the historian seeks to answer. In making preliminary judgments about the usefulness of primary historical sources, historians usually adopt the principle of immediacy--that is, the closer the source is in time and place to an episode under investigation, the better the source.

Every source is biased in one way or another and must therefore be scrutinized skeptically and critically. Every individual piece of evidence (source) must also be carefully scrutinized and cross-checked with other evidence. The historian must think about who is producing any given source and what his or her purpose was in producing it. The relevance of this stricture is probably most obvious with respect to sources that try to persuade the reader or attempt to justify an individual's actions: political speeches, party platforms, newspaper editorials, autobiographies of famous persons. Yet it applies equally well to other types of sources.

As an example, consider the U.S. federal census of population, virtually without peer among national government censuses as a long-term time series of statistical information. However, the census is not as comprehensive as its compilers, funders, or users would wish. Some people do not voluntarily participate in the census--believing, for example, that their privacy will be violated or that they should not participate because they are foreign nationals. Others simply forget to fill out or return the forms. Some make errors when completing the forms, although many of these are now caught by the Census Bureau. When census enumerators go out into the field, some people are difficult to find, their neighbors cannot supply accurate information, or, in our highly mobile society, people have recently moved. Sometimes enumerators fear going into certain neighborhoods because they are reputed to be dangerous.

Historically, these problems were arguably even greater because the census was conducted by amateurs who may have been political appointees or have had little training. Census canvassers were sometimes paid by the entry (the more people they found, the more money they earned), which encouraged overcounting. The point is that all sources, even one of such generally high quality as the U.S. federal census, have their limitations as well as their virtues.

If students are to use primary sources--and we believe they should--they must be taught to deal with issues of reliability, bias, and accuracy. A lesson I have developed and used to teach about source evaluation is available on the Learning Page: The Historian's Sources.

As we grapple with original sources, we can hardly escape the conclusion that these documents tell us, in contemporaries' own words, about real people who faced real problems and issues in real situations. We discover that they, like ourselves, made decisions and solved problems with less-than-perfect information at their disposal; they did not know, any more than we can know, what the outcomes of their actions or solutions might be. We also learn that these people, no matter how different they may be in some respects, were not totally unlike us either. We also discover that human history is not inevitable; it is ultimately about humans making choices.

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