This paper sets out to study the second person–number marking in the (indicative) simple past in the history of European Portuguese, with a particular focus on morphological innovations such as fostes tu, which are considered deviant. These innovations, according to some brief descriptions in the literature (cf. Piel 1989; Williams 1994), are considered a case of morphological change by analogy; however, it remains to be determined whether it is a case of analogical extension or, possibly, leveling that would have resulted in syncretism. Based on data retrieved from private letters from the 16th to the 20th century by almost illiterate authors, we will argue that this innovation results from an analogical extension, motivated by morphological and pragmatic factors.