How do students and historians gain an understanding of events in the past? They do it through consulting sources (usually a document of some kind). Sources include books, photographs, letters, diaries, newspaper articles, magazines and journals, sound recordings, web sites, and e-mail messages.
Historians and other students of the past divide documents into two main categories: Primary Sources and Secondary Sources. When trying to understand events in the past, it is critical for you to know which type of source you are dealing with.

A Primary Source is a document that was created at or near the time of the event that it discusses. Often it is the account of a participant or eyewitness to an event. Examples of primary sources are letters, diaries, laws and other acts of governments, e-mail messages, recordings, and newspaper articles. Primary sources can be either published or unpublished. A handwritten letter from an American soldier in Afghanistan to someone back home would be an unpublished primary source for a future historian of the war in Afghanistan. If a book publisher collected a number of soldiers' letters and printed them as a book, each letter in the book would be a published primary source.

Secondary Sources are accounts of events written by historians or other observers, after or at some distance from the event itself. A history of the American Revolution (1775-1783) written in 2002 or 1890 would be a Secondary Source. In most cases, Secondary Sources offer explanations and interpretations of historical events. These interpretations usually are based on a study of Primary Sources.

As an example, imagine that you wanted to learn about the surrender of the British army at Yorktown in 1781. It would be nice to be able to hear a recording of an interview with the generals and soldiers who took part in the battle. Because sound recordings did not exist in this period, we generally have to rely on written primary sources. Some written primary sources that you might consult would be the reports of the commanders of the two armies, the text of the surrender agreement, letters and diaries of soldiers in each army, and newspaper accounts of the surrender in American and British newspapers. Secondary sources would include histories of the American Revolution or books or encyclopedia articles (on-line or printed) on the Yorktown campaign.

Historians and students need to view all kinds of sources with a critical eye. With Primary Sources, you should ask questions of yourself like: Was the author of this document in a good position to observe what she is writing about? Were there other observers of the battle who for one reason or another were unable to write down what they saw? Are there other ways to reconstruct their perspectives? With both Primary and Secondary Sources, you should always ask whether the author is biased in some way-does the author have a point he is trying to prove? Always think about where the author is coming from. For example, imagine a historian is studying the career of Eminem. She has before her the following: an article on Eminem in People magazine; a press release from Eminem's record label; and the text of the "Communications Decency Act." The authors of each document have distinct points of view, possibly biases. You as a student should think through what those points of view and biases might be.

Remember that the form a document appears in does not define its nature as Primary or Secondary. A Secondary Source is almost always a published document. A Primary Source can be published or unpublished. Just because something is printed between the covers a book, it is not necessarily a Secondary Source. Often diaries, letters, public laws and the like are published. They are still Primary Sources.