A number of Western Mande languages, viz. most Greater Manding varieties and Soninke, differ from the rest of Mande in that in clauses with certain TAM and polarity (TAMP) values, they use different TAMP markers depending on the transitivity status of the clause. The range of predicative constructions involved varies according to the language. It may include positive constructions, such as Positive Perfective, as in (1) from Mandinka, Positive 2PL Imperative, Positive Imperfective with focalization, Positive Subjunctive, as well as negative constructions, such as Negative Perfective, as in (2) from Mandinka, Negative Imperfective and Negative Progressive. I provide a diachronic explanation for this typologically unusual situation by arguing that depending on the construction, TAMP marking conditioned by transitivity status in Western Mande has developed following two different pathways. The first involves all the positive constructions, with the exception of the Subjunctive. Here, the difference in TAMP marking conditioned by transitivity status results from a conflation of two different constructions, viz. C1 that used to function primarily as intransitive and C2 that used to be largely indifferent to transitivity status. Along with the integration of C1 and C2 as variants of the new construction C', C1 has further specialized as a dedicated intransitive construction, the intransitive variant C'I of the new construction C'; and C2 has become confined to transitive uses as the transitive variant C'T of C'. The second group of constructions includes all the negative constructions and the Positive Subjunctive. Here, the difference in TAMP marking is only indirectly related to the transitivity status of the construction. It is a result of a differential phonological evolution of a single TAMP marker as a function of its right context, which is accounted for by frequency effects and typical patterns of Mande phonotactics. In particular, the TAMP marker in the intransitive variant of a given construction has preserved some segmental or tonal material that has been lost in the allomorph in the transitive variant of the construction.