Finite verb to be omitted. For example, in the Latin sentence "cogito ergo sum" ("I think therefore I am") the finite verbs "cogito" and "sum" appear without an explicit subject – the subject is understood to be the first-person personal pronoun, and this information is marked by the way the verbs are inflected. In English, finite verbs lacking subjects are normal in imperative sentences: And also occur in some fragmentary utterances: The relatively poor system of inflectional morphology in English makes the central role that finite verbs play be often not so evident. In other languages, finite verbs are the locus of
Cogito, ergo sum ("If I am mistaken, I am") (book XI, 26), and also anticipates modern refutations of the concept. Furthermore, in the "Enchiridion" Augustine attempts to refute skepticism by stating, "[B]y not positively affirming that they are alive, the skeptics ward off the appearance of error in themselves, yet they do make errors simply by showing themselves alive; one cannot err who is not alive. That we live is therefore not only true, but it is altogether certain as well" (Chapter 7 section 20). In 1640 correspondence, Descartes thanked two colleagues for drawing his attention to Augustine and notes similarity and difference.