Spanish has three verb classes, identified by three different theme vowels: -a, e, and -i. The verbs show three different types of paradigm levelling, whereby verb class distinctions are neutralised, either in whole or in part. These three types of levelling interact in a nontrivial manner with patterns of root allomorphy. I analyse both the levellings and the correlations with root allomorphy in terms of the nanosyntactic root size paradigm, which assumes that differences in the size of root are responsible for the choice of the theme vowel. The levellings will be shown to follow from possible variations in root size of verbs internal to a single verb class, causing roots to `shrink', and become the same size as the roots of another verb class. As a result, they behave like the verbs of that other class, giving rise to the levelling phenomenon.
Guido Vanden Wyngaerd (Mon,) studied this question.