Although primary sources always refer to sources containing original information, distinction varies between subject areas and disciplines.

In the Humanities, journal articles are often considered to be secondary sources because they may discuss, critique, or analyze an original creative work by an author (such as a novel in the field of English). Likewise, within the discipline of History, many newspaper articles are considered to be primary sources because they report events as they are happening (or as they are being created). This treatment is quite a contrast to the Sciences where newspaper articles are not used as sources.

The important concept to remember when identifying primary sources is not what format they are in (which varies), but whether they contain original information or creative works for the discipline in question.