A central problem for pro drop theory is how to account for the distribution of argumental null subjects. A paradigmatic approach, in which the whole paradigm determines whether a language can have null subjects or not, undergenerates in that it does not predict the existence of partial pro drop languages. An approach in which the licensing of null subjects is determined per context overgenerates in that it is not obvious why e.g. English does not have null subjects in at least the 3rd person singular. In this talk, we aim at repairing the overgeneration problem for contextual approaches. By contrasting the Romance pro drop languages Spanish, Italian and Romanian with Germanic languages and Standard French, we argue that only the latter express tense and agreement with the same underlying morpheme, which therefore contains features (tense) that are incompatible with the subject it would have to license: it is featurally overspecified. The question is then what determines the choice between a bi- or monomorphemic expression of tense and agreement, and we will argue that reasonable assumptions about the acquisition of morphological systems makes the right cut.