An author must provide a source for every direct quotation (other than an extremely well known quote) and for every table, graph, and illustration that is reproduced from someone else's work.1 Sources must also be cited for all facts, statistics, conclusions, and opinions that the author obtained from someone else's published or unpublished work. Sources are not needed, however— and should not be given—for facts that are in general circulation.
The means by which an author cites the source of a quotation, paraphrase, or piece of evidence taken from another work depends on
the conventions within the author's profession or field
the intended audience for the work (e.g., scholars, professionals, general readers)
the number and complexity of citations within the author's manuscript
the preferences, if any, of the publisher
For uniformity within their issues, all journals and magazines impose their house style on contributors. Some book and corporate publishers do so as well, especially for multi-author collections and works in a series. Other publishers allow authors to use whatever citation system they prefer, as long as it is not too idiosyncratic and is applied consistently.____________________