When you cite more than one source parenthetically, the order of those sources (alphabetic, by importance, by date) is up to you.

For instance, if Michel Foucault is more important to your discussion than Roland Barthes, you could place Foucault’s name first in the following parenthetical citation:

Starting in the 1960s, several French philosophers began challenging the traditional concept of the author (Foucault; Barthes).

However, if both authors are equally important to your discussion, you might choose to order them alphabetically:

Starting in the 1960s, several French philosophers began challenging the traditional concept of the author (Barthes; Foucault).

 

Works Cited

Barthes, Roland. “The Death of the Author.” Image, Music, Text, translated by Stephen Heath, Hill and Wang, 1977, pp. 142–48. 

Foucault, Michel. “What Is an Author?” Aesthetics, Method, and Epistemology, edited by James D. Faubion, translated by Robert Hurley et al., New Press, 1998, pp. 205–22. Vol. 2 of Essential Works of Foucault, 1954–1984.