Pronominal affixes in polysynthetic languages have an ambiguous status in the sense that they have characteristics normally associated with free pronouns as well as characteristics associated with agreement markers. This situation arises because pronominal affixes represent intermediate stages in a diachronic development from independent pronouns to agreement markers. Because this diachronic change is not abrupt, pronominal affixes can show different characteristics from language to language. By presenting an in-depth discussion of the pronominal affixes of Yurakaré, an unclassified language from Bolivia, I argue that these so-called intermediate stages as typically attested in polysynthetic languages actually represent economical systems that combine advantages of agreement markers and of free pronouns. In terms of diachronic development, such ‘intermediate’ systems, being functionally well-adapted, appear to be rather stable, and it can even be reinforced by subsequent diachronic developments.