Where do conjugated infinitives come from?

Although conjugated infinitives (CIs) occur in languages as diverse as Portuguese, Welsh, Hungarian, and West Greenlandic, the prototypical infinitive is nonfinite in the traditional sense: it has no subject person agreement. This paper argues that CIs are special in the sense that they cannot arise spontaneously in the course of language acquisition. Even in languages with obligatory agreement, CIs require salient triggers. Two common sources are identified: (1) purposive subjunctives; (2) pronominal elements (e.g., construed with a nominalization). These sources require one of two kinds of reanalysis, generally based on a surface ambiguity. In all of the cases documented here, more than one of these factors interacted to trigger a CI.