AbstractThis study focuses on the grammaticalization of agreement markers from possessive pronouns, which has two different dimensions: loss of referentiality (function) and loss of morpho‐phonological independence (form). I examine the referential potential and formal expression type of possessive person markers in a worldwide sample of 39 languages with an alienability distinction. Referential potential is measured independently of expression type by applying a new typology of person markers. First, I demonstrate that inalienable possessive marking is at least as referential and formally independent as alienable possessive marking, and often less referential and less independent. Unlike explanations in terms of frequency and iconicity, I argue that this asymmetry is essentially semantics‐based: the presence of a possessive relationship is inherent to the meaning of the inalienable noun, which is therefore in less need of expressive marking than alienable nouns. Second, I show that loss of referentiality correlates with loss in form, but in a relative rather than an absolute sense: in individual languages, higher referential markers never show a greater degree of bonding with the possessee than lower referential markers. These results suggest that function and form evolve in the same direction, but need not evolve at the same pace.