Current theories on the nature and history of the Chadic verbal system claim that Proto-Chadic had (aa fundamental binary distinction of aspect, in which (b) the Perfective was the unmarked category, and that (c) a characteristically marked Imperfective verb stem can be reconstructed for the proto- languageThis paper presents comparative evidence from 10 languages of the Biu- Mandara branch of Chadic, on the basis of which all three claims are rejectedThe existence of dichotomous aspect systems in some modern Chadic languages is explained by and related to essentially three simplification and / (or) elaboration processes which are attributed to the linguistic history of the in dividual branches of the family: (1) loss of stem- final marking de vices with compensatory shift to preverbal marking (2) redesignation of the proto-verbal noun, and (3) redesignation of verbal plurals.