This dissertation proposes a theory of temporal implicatures, and applies it to the study of tense in Mbya Guarani. It is composed of two parts. In the first one, I discuss the analyses of temporal implicatures developed by Musan (1995, 1997) and Magri (2009). Although I argue in favor of Magri's (2009) analysis, I reject two aspects of his proposal: that tense is universally or generically qua...