Mutation in Welsh

The XP Trigger Hypothesis is a widely accepted account of syntactic mutation in Welsh which states that mutation, a regular alternation in form of the initial segment of a word, occurs if a word is positioned after the right edge of an XP (with some additional framework-specific structural constraints). The XP Trigger Hypothesis poses a problem for Lexical-Functional Grammar (LFG) because it presupposes the existence of empty categories. Null subjects and wh-traces both ‘count’ as XPs for the purposes of the XP Trigger Hypothesis, and therefore must be represented in the tree structure. Such empty categories are generally not represented as XPs in the tree in LFG, being represented only at f-structure. In my analysis, I show that it is possible to account for the data of the XP Trigger Hypothesis without presupposing the existence of empty categories, instead using phrase-structural rules and f-structural relationships between words to predict mutation.