model, this is in fact a characteristic typical of linkages and dialect continuums generally: this has been an argument for approaching this family with the tools based on the Wave model, including dialectology and Historical glottometry. What follows is a sample of some significant linguistic traits (innovations since Vulgar Latin) that run across the Romance linkage. The differences among Romance languages occur at all levels, including the sound systems, the orthography, the nominal, verbal, and adjectival inflections, the auxiliary verbs and the semantics of verbal tenses, the function words, the rules for subordinate clauses, and, especially, in their vocabularies. While most of those differences are clearly due to independent development after the breakup of the Roman Empire (including invasions and cultural exchanges), one must also consider the influence of prior languages in territories of Latin Europe that fell under Roman rule, and possible heterogeneity in Vulgar Latin itself. Romanian, together with other related languages, like Aromanian, has a number of grammatical features which are unique within Romance, but are shared with other non-Romance languages of the Balkans, such as Albanian, Bulgarian, Greek, Macedonian, Serbo-Croatian and Turkish. These include, for example, the structure of the vestigial case system, the placement of articles as suffixes of the nouns ( = "sky", = "the sky"), and several more. This phenomenon, called the Balkan language area, may be due to contacts between those languages in post-Roman times. Formation of plurals Some Romance languages form plurals by adding (derived from the plural of the Latin accusative case), while others form the plural by changing the final vowel (by influence of Latin nominative plural endings, such as ) from some masculine nouns. Plural in : Portuguese, Galician, Spanish, Catalan, Occitan, Sardinian, Friulian, Romansh. Special case of French: Falls into the first group historically (and orthographically), but the final -s is no longer pronounced (except in liaison contexts), meaning that singular and plural nouns are usually homophonous in isolation. Many determiners have a distinct plural formed by both changing the vowel and allowing in liaison. Vowel change: Italian, Neapolitan, Sicilian, Romanian. Words for "more" Some Romance languages use a version of Latin plus, others a version of magis. Plus-derived: French , Italian , Sardinian , Piedmontese , Lombard , Ligurian , Neapolitan Friulian , Romansh , Venetian . In Catalan is exclusively used on negative statements in Mallorcan Catalan dialect, and "" is the word mostly used.