Non-written historical sources should not be utilized to write history. Historiography's topic is history itself. Historiography is the study of how history is written and how our knowledge of history evolves through time. History books contain narratives about important people and events in the past, but they are not considered primary sources because they weren't recorded immediately after the fact. Written records exist for anyone who was rich or powerful enough to hire historians to record their lives for them. These records include letters, diaries, official documents (such as treaties), and memoirs. Non-primary sources can give us insights into how history was experienced by ordinary people, but they cannot replace primary sources. Primary sources are documents that have been directly copied from other documents, usually earlier versions of them. For example, a letter written by an ancestor of mine called William Henry Harrison is a primary source because it was copied from a copy of the original letter he wrote years before when he was elected president under the name William Henry Harrison. Secondary sources include works of history that were not written by people who lived during the period being studied; rather, they are based on primary sources such as letters, journals, and official documents. Tertiary sources include anything else you might want to use as evidence for your argument.