This thesis explores the status of a specific subset of absent characters within twentieth century American drama. By borrowing the term “proximate cause” from tort law and illuminating its intricacies through David Hume’s A Treatise of Human Nature, this thesis re-appropriates proximate cause for literary studies. Rather than focus on characters whose existence remains the subject of critical debate, this set of absent characters presumably exists but never appear onstage. Despite their non-appearance onstage, however, these absent characters nonetheless have a profound effect upon the action that occurs during their respective plays. Highlighting the various ways in which these characters serve as the proximate cause for the onstage action of a given play will expand the realm of drama and literary studies in myriad ways.