There is a broad consensus within linguistics that personal pronouns may undergo grammaticalization to yield person agreement morphology. Furthermore, it is widely assumed that similar processes apply to both subject and object pronouns. In this chapter I consider the fate of a phonologically identical set of clitic pronouns in Middle West Iranian languages, which were deployed in both subject and object indexing. The modern outcomes have been rather different; while erstwhile clitic subject pronouns have spawned subject agreement morphology in some languages, these clitic pronouns have not yielded obligatory object agreement in the category of person in any Iranian language. Neither traditional grammaticalization theory, nor recent formalizations of grammaticalization within Minimalism, offer a compelling explanation for this asymmetry. I suggest it reflects a fundamental difference in the informativity of subject as opposed to object indexing with respect to the category of person, as opposed to that of gender and number.