Online Encyclopedia
Secondary source
Secondary sources, in the study of history, are those writings which were not penned contemporaneously with the events in question.
It is a contrast with a primary source, which is some form of information which can be taken as an artifact of its times. A secondary source is often a commentary or analysis of a primary source. For examples, the diary of General Ulysses S. Grant is a primary source, because it was penned in its time and can be taken as a raw, original source of information (which does not say anything about its veracity or completeness). A book which writes about Grant, and uses Grant's diary, would generally be a secondary source. In historiography, however, even this book could be a primary source: if another author was writing on the many histories written about Grant, they may be using what were originally conceived of as secondary sources as artifacts themselves.
A primary source is not, by default, more authorative or accurate than a secondary source. Secondary sources often are subjected to peer review, are well documented, and are often produced through institutions where methodological accuracy is important to the future of the author's career and reputation. A primary source like a journal entry, at best, only reflects one person's take on events, which may or may not be truthful, accurate, or complete. Historians subject both primary and secondary sources to a high level of scrutiny.
As a general rule, however, modern historians prefer to go back to primary sources, if available, as well as seeking new ones. Primary sources, whether accurate or not, offer new input into historical questions and most modern history revolves around heavy use of archives for the purpose of finding useful primary sources. A work on history is not likely to be taken seriously if it only cites secondary sources, as it does not indicate that original research has been done.