Its grammar evolved from Common Slavic, with complex inflection, preserving seven grammatical cases in nouns, pronouns, and adjectives. Verbs exhibit imperfective or perfective aspect, with a moderately complex tense system. Serbo-Croatian is a pro-drop language with flexible word order, subject–verb–object being the default. It can be written in Serbian Cyrillic or Gaj's Latin alphabet, whose thirty letters mutually map one-to-one, and the orthography is highly phonemic in all standards. Serbo-Croatian generally goes by the individual names Serbian, Croatian, Bosnian, and sometimes Montenegrin and Bunjevac. In the language itself, it is typically known as / "Serbo-Croatian", / "Croato-Serbian", or simply / "ours". Throughout the history of the South Slavs, the vernacular, literary, and written languages (e.g. Chakavian, Kajkavian, Shtokavian) of the various regions and ethnicities developed and diverged independently. Prior to the 19th century, they were collectively called "Illyric", "Slavic", "Slavonian", "Bosnian", "Dalmatian", "Serbian" or "Croatian". Since the nineteenth century the term "Illyrian" or "Illyric" was used quite often (thus creating confusion with the Illyrian language). Although the word "Illyrian" was used on a few occasions before, its widespread usage began after Ljudevit Gaj and several other prominent linguists met at Ljudevit Vukotinović's house to discuss the issue in 1832. The term "Serbo-Croatian" was first used by Jacob Grimm in 1824, popularized by the Viennese philologist Jernej Kopitar in the following decades, and accepted by Croatian Zagreb grammarians in 1854 and 1859. At that time, Serb and Croat lands were still part of the Ottoman and Austrian Empires. Officially, the language was called variously "Serbo-Croat, Croato-Serbian, Serbian and Croatian, Croatian and Serbian, Serbian or Croatian, Croatian or Serbian." Unofficially, Serbs and Croats typically called the language "Serbian" or "Croatian", respectively, without implying a distinction between the two, and again in independent Bosnia and Herzegovina, "Bosnian", "Croatian", and "Serbian" were considered to be three names of a single official language.