Former US Secretary of Defense Donald Rumsfeld famously said,
Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns— the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones.
Although that is the famous part of the dialogue, later in the same briefing Rumsfeld said something even more interesting for historians: “I could have said that the absence of evidence is not evidence of absence, or vice versa.”
When searching for sources, how can researchers handle the unknown/ unknowns and the known/ unknowns? First of all, let's dispel three myths: “total archives”; archival exclusion of evidence from social margins; and claims of archival “objectivity.”
Antoinette Burton in her introduction to Archive Stories writes that there is a “commonly held belief in the power of a ‘total archive’ “ (Burton, 2005, 18). Hardly. The concept known as “total archives” came from Canada, where it meant “that publicly funded archival institutions— such as national archives, provincial archives, and city archives— would acquire, preserve, and make available for public use both government and private sector records in all media, including paper documents and visual and cartographic images, sound recordings, and in more recent years, magnetic and digital media” (Millar, 1998). However, as Laura Millar writes in an article drawn from her dissertation on the “total archives” concept in English Canada:
This concept of total archives, while not unique to Canada, differed significantly from archival practice in many other jurisdictions. The United States has evolved a tradition of separating the care of public and private records between state archives, on the one hand, and historical societies and university libraries on the other. British and European practice, particularly at the national level, has also divided the preservation of public and private sector records between agencies such as England's Public Record Office, France's Archives de France, or Germany's Bundesarchiv and these countries’ national libraries, university libraries, and state and local historical societies.