Classical Latin followed by Late Latin
Classical Latin is the form of Literary Latin recognized as a literary standard by writers of the late Roman Republic and early Roman Empire. It was used from 75 BC to the 3rd century AD, when it developed into Late Latin. In some later periods, it was regarded as good or proper Latin, with following versions viewed as debased, degenerate, or corrupted. The word Latin is now understood by default to mean "Classical Latin"; for example, modern Latin textbooks almost exclusively teach Classical Latin.
Cicero and his contemporaries of the late republic referred to the Latin language, in contrast to other languages such as Greek, as lingua latina or sermo latinus. They distinguished the common vernacular, however, as Vulgar Latin (sermo vulgaris and sermo vulgi), in contrast to the higher register that they called latinitas, sometimes translated as "Latinity". Latinitas was also called sermo familiaris ("speech of the good families"), sermo urbanus ("speech of the city"), and in rare cases sermo nobilis ("noble speech"). Besides the noun Latinitas, it was referred to with the adverb latine ("in (good) Latin", literally "Latinly") or its comparative latinius ("in better Latin", literally "more Latinly").
Latinitas was spoken and written. It was the language taught in schools. Prescriptive rules therefore applied to it, and when special subjects like poetry or rhetoric were taken into consideration, additional rules applied. Since spoken Latinitas has become extinct (in favor of subsequent registers), the rules of politus (polished) texts may give the appearance of an artificial language. However, Latinitas was a form of sermo (spoken language), and as such, retains spontaneity. No texts by Classical Latin authors are noted for the type of rigidity evidenced by stylized art, with the exception of repetitious abbreviations and stock phrases found on inscriptions.