a referent in a nonreal 'world' or mental space (desire, hypothetical, negative, etc.) whose individual identity is unknown to speaker and hearer; all that is known about the nonreal referent is its type, as provided by the common noun and any modifiers in the referring phrase. Example: in An undergraduate student may take this course, all that is known about the possible referent is that he or she belongs to the type 'undergraduate student'. (Section 3.5)