APA requires you cite the authors or source every time you refer to about their work. Depending on how you cite or construct the sentence, the last name of the two authors and the year of publication should be included. When your material of reference or source has two authors, you need to cite both names every time you refer to their work.
APA In-Text Citation Two Authors Printed Book
If the names are referred to in the text, then only the year appears in the parenthesis. Use the same format as you would for one author, except that you always include both authors’ names whenever you cite the source in your paper. (APA 6th, pp. 174-177)
Gray and Johnson (2009) studied motor inhibition in baseball players.
Baker and Hamilton (2007) found a high rate of depression in the participants.
Brabant and Mooney (1986) have used the comic strip to examine evidence of sex role stereotyping.
Smith and Johnson (2012) found that one in three dogs is morbidly obese.
If the names are not referred to in the text, include the names in the parenthetical reference joined by an ampersand (&).
Complex motor skills were studied in a baseball batting simulation (Gray & Johnson, 2009).
A high rate of depression was found among the participants (Baker & Hamilton, 2007).
The comic strip has been used to examine evidence of sex role stereotyping (Mooney & Brabant, 1986).
APA End Reference Citation Two Authors Printed Book
List by their last names and initials. Use the ampersand instead of the and. (APA 6th p. 175)
Lincoln, Y. S., & Guba, E. G. (1985). Naturalistic inquiry. Newbury
Park, CA: Sage.
Strunk, W., Jr., & White, E. B. (1979). The guide to everything and
then some more stuff. New York, NY: Macmillan.
Gregory, G., & Patty, T. (2006). Designing brain compatible learning
(3rd ed.). Thousand Oaks, CA: Corwin.
Mitchell, T. R., & Larson, J. R. (1987). People in organizations: An
introduction to organizational behavior (3rd ed.). New York, NY: McGraw-Hill.