Multiple Sources for One Idea
Several of the most common documentation formats require the use of a semicolon between the different sources within the citation when both reference the same concept. In American Psychological Association style, place commas between the authors and dates but semicolons between the different sources: (Adams, 2000; Haven, 2010). Harvard style also includes authors and dates in citations but with no punctuation between. Again, place a semicolon between references: (Adams 2000; Haven 2010). For Modern Language Association style, omit punctuation in citations except for semicolon between sources: (Adams 22; Haven 314). For the footnote or endnote style of Chicago formatting, each superscript number refers to a single source, so put appropriate superscript numbers for each source at the end of the borrowed material from that particular source.
Citations Within One Sentence
If a single sentence in your research paper includes multiple ideas from different sources, clarify which information comes from which source by placing parenthetical citations near the ideas they refer to. An example might look like this in APA or Harvard style:
According to Kellerman (2011), few teachers follow such guidelines, although Lambdin (2009) disagrees.
MLA style would look the same except without the dates, and Chicago style would include the superscript numbers, one for Kellerman after "guidelines" and one for Lambdin at the end of the sentence.