Whether conducting research in the social sciences, humanities (especially history), arts, or natural sciences, the ability to distinguish between primary and secondary source material is essential. Basically, this distinction illustrates the degree to which the author of a piece is removed from the actual event being described, informing the reader as to whether the author is reporting impressions first hand (or is first to record these immediately following an event), or conveying the experiences and opinions of others-that is, second hand.
These are contemporary accounts of an event, written by someone who experienced or witnessed the event in question. These original documents (i.e., they are not about another document or account) are often diaries, letters, memoirs, journals, speeches, manuscripts, interviews and other such unpublished works. They may also include published pieces such as newspaper or magazine articles (as long as they are written soon after the fact and not as historical accounts), photographs, audio or video recordings, research reports in the natural or social sciences, or original literary or theatrical works.
The function of these is to interpret primary sources, and so can be described as at least one step removed from the event or phenomenon under review. Secondary source materials, then, interpret, assign value to, conjecture upon, and draw conclusions about the events reported in primary sources. These are usually in the form of published works such as journal articles or books, but may include radio or television documentaries, or conference proceedings.