Historians arrange information and interpret historical stories. History is a valuable resource for learning lessons from our forefathers' moral, ethical, political, social, and administrative acts and decisions. As a result, themes are crucial when historians chronicle historical occurrences. Historians use themes to help them understand what happened in history and why it mattered at the time it did. Themes also influence how historians write about specific people or events. In order to tell a coherent story about something that happened in history, historians need to know its date, place, and participants. They also need to know the underlying causes of what took place. These factors determine how historians interpret events in their source materials (letters, journals, books, films, etc.). By understanding these sources within their historical context, they are able to draw conclusions about what happened during certain periods in time and why it was important at the time it was happening. For example, when historians study American slavery they want to know how it began, who were the main players involved, and how it affected the lives of those who were enslaved and those who owned them. Using these questions as a guide, historians can examine primary source documents such as letters, diaries, and official government reports to learn more about slavery. They can also look at secondary sources such as books and articles written by other historians for similar information.