Published online by Cambridge University Press: 28 November 2008
In an important theoretical discussion, Sampson (1975) argues against what he terms the ‘single-mother condition’. This is the condition that no node may have more than one mother. It is central to the definition of a tree, as the term is normally understood in linguistic theory. Sampson argues that the condition should be abandoned, and that what he terms ‘semitrees’, graphs in which nodes have more than one mother, should be permitted as representations of linguistic structure.2 He argues for this innovation on the basis of certain anaphoric phenomena. In this note, I want to take a critical look at his argument. I will suggest that the semitree approach to anaphoric phenomena that he sketches is untenable, and hence that these phenomena provide no motivation for an abandonment of the single-mother condition.