Full Idea
Direct reference is commonly effected by the use of proper names and indexical expressions, and sometimes by what has been called (by Donnellan) the 'referential' use of descriptions.
Gist of Idea
Direct reference is by proper names, or indexicals, or referential uses of descriptions
Source
Robert Merrihew Adams (Primitive Thisness and Primitive Identity [1979], 2)
Book Reference
'Metaphysics - An Anthology', ed/tr. Sosa,E. /Kim,J. [Blackwell 1999], p.174
A Reaction
One might enquire whether the third usage should be described as 'direct', but then I am not sure that there is much of a distinction between references which are or are not 'direct'. Either you (or a sentence) refer or you (or it) don't.