Although such gaps have been known to us since the days of Classical grammarians, they remain poorly understood. Defectiveness contradicts basic assumptions about the way inflectional rules operate, because it seems to require that speakers know that for certain words, not only should one not employ the expected rule, one should not employ any rule at all. This is a serious problem, since it is probably safe to say that all reigning models of grammar were designed as if defectiveness did not exist, and would lose a considerable amount of their elegance if it were properly factored in.
This volume addressed these issues from a number of analytical approaches - historical, statistical and theoretical - and by using studies from a range of languages.