Abstract
Verbs lacking a 1SG non-past (such as убедить) are a familiar problem in Russian morphology. While it can be argued that defectiveness is lexicalized, the question remains as to how this came about diachronically. This paper assesses the historic evidence. Contemporary defectives can be traced to two earlier classes of verbs which had aberrant alternations in the 1SG: (i) verbs with Church Slavonic д ~ жд, and (ii) dental stem verbs which lacked alternation altogether. Particular attention is paid to the latter type, as it has not yet received comprehensive scholarly treatment. The origin of defectiveness is traced to the suppression of these two classes over the last two centuries: lexical specification of an aberrant morphological alternation is replaced by lexical specification of a gap.