The paper investigates the conditions that determine the distribution of object pronouns in the period before the latter become fixed to the post-verbal position. In the transition between Old English and Early Middle English (henceforth OE and EME), object pronouns surface to the left of T, to the left of V and to the right of V. It will be shown that the distribution in the pre-T and post-V positions in OE is due to information structural and prosodic interface conditions, whereas the position at the left of V is analysed as unmarked. In EME, the pre-T position continues to be linked to topicalization, whereas the pre-V position shows a progressively less frequent distribution. The post-verbal mapping of object pronouns can still be linked to prosodic 1 and information structural (IS) mapping conditions, but the data show that the post-verbal position was on the way to being reanalysed as the unmarked position. The change will be attributed to two factors: a) the new option of de-accentuation in situ, leading pronouns to choose the non-finite verb as their phonological host, and b) the grammaticalization of the definite determiner that renders light (non-branching and left-branching) objects into right-branching, heavy objects at the end of the OE period. We will provide evidence that it is the latter factor that leads to the new option of de-accenting pronouns in situ (cf. Hinterhölzl 2017).