Several scholars have studied the origin of gender in classification of nouns. Wurzel (1992), examining systems for classifying nouns in Vietnamese, Swahili, and Latin, suggests that gender systems are originally semantically determined. As they develop, he suggests, they become less semantically defined. Less is known about the origins of semantically based systems of classifying verbs and the morphology that expresses these classifications. This raises the following questions: Where does semantically based classifying morphology in verbs come from? Does it become less semantically defined over time?

In this paper I examine morphosemantic classes of verbs — transitive, unergative, and unaccusative — from this point of view. I believe that because the changes involved in these examples are on-going, attested, or recent, many aspects of the origins of these systems are transparent. In Udi, a member of the North East Caucasian language family, this classification is one of the two cross-cutting semantic systems of classification of verbs. Here the morphological classes derive from a semantic distinction previously realized in the syntax, and in some ways this origin is quite parallel to what has been proposed for gender. I also examine the very different origins of the morphology of verb classification in Georgian. I argue that verb classes have not (yet) become less semantically motivated, but that in Udi the semantic motivation has changed.