Facts in literature
English teachers generally consider what an entire class
knows to be common knowledge. If students have just read Romeo
and Juliet, it is common knowledge that Shakespeare is the author,
that the play is set in Verona, that Tybalt kills Mercutio and Romeo
Tybalt, that the lovers are married and die. In an essay about the
play, a student would not need to give a source for Shakespeare's
authorship or the location in the play of any of these plot
elements--or even more specific ones (the first conversation between Romeo
and Juliet is in the form of a sonnet with an elaborate extended
metaphor). Of course the student would have to give the
location of any words or lines quoted from the play.
As in writing for the history department,
historical names, dates, and events that one can find in any standard
reference work are considered common knowledge. Thus, it is common
knowledge that Shakespeare was born in 1564 (probably), that he moved to
London and was an actor and playwright, and that he returned to Stratford
and died in 1616.
Of course how one knows that something is
common knowledge is an interesting question. A student researching
an author's life would certainly want to consult at least three sources and
compare notes--and any item about which sources are in disagreement would
fall outside the realm of common knowledge.
In order to feel certain of the facts detailed in essays or
projects, English teachers will nearly always require that students
include with an essay or project a list of works consulted--the works from which they learned
Facts supporting an argument
In theory, a fact about such controversial
issues as capital punishment or abortion might also fall in the realm of
common knowledge (if one can find the fact in any standard reference
work). In practice, there is often disagreement about such facts,
and one can only strengthen an argument by citing the sources that support
it. Therefore, in persuasive writing it is best to cite sources for
all but the most obvious facts. For example, while it is common knowledge
that the period of human gestation is nine months, the point at which a
fetus is viable outside the womb is a matter about which authorities
disagree--and so it is best to cite the source for such information.
What is not common knowledge: criticism
Even if all the students in a class read a
critical essay about a work, the ideas in that work are not common
knowledge--because we always give credit to others for their ideas.
Thus, wherever students read ideas about a work of literature--whether in
scholarly essays or study guides like Cliff's Notes or on the
Internet--they must give the source for these ideas. Clearly,
then, there is some advantage in avoiding secondary sources: students can
credit for their thoughts about a work of literature without wondering if
they may have read them somewhere else.