In scholarship, a secondary source is a document or recording that relates or discusses information originally presented elsewhere. A secondary source contrasts with a primary source, which is an original source of the information being discussed; a primary source can be a person with direct knowledge of a situation or a document created by such a person.
A secondary source is one that gives information about a primary source. In this source, the original information is selected, modified and arranged in a suitable format. Secondary sources involve generalization, analysis, interpretation, or evaluation of the original information.
The most accurate classification for any given source is not always obvious. Primary and secondary are relative terms, and some sources may be classified as primary or secondary, depending on how they are used. A third level, the tertiary source, such as an encyclopedia or dictionary, resembles a secondary source in that it contains analysis, but attempts to provide a broad introductory overview of a topic.
Information can be taken from a wide variety of objects, but this classification system is only useful for a class of sources that are called symbolic sources. Symbolic sources are sources that are intended to communicate information to someone. Common symbolic sources include written documents such as letters and notes, but not, for example, bits of broken pottery and scraps of food excavated from a midden, regardless of how much information can be extracted from an ancient trash heap, or how little can be extracted from a written document.
Many sources can be considered either primary or secondary, depending on the context in which they are used. Moreover, the distinction between primary and secondary sources is subjective and contextual, so that precise definitions are difficult to make. For example, if a historical text discusses old documents to derive a new historical conclusion, it is considered to be a primary source for the new conclusion, but a secondary source of information found in the old documents.