OK so while doing research on the German reigning houses I came across something confusing. Most sources I read call the non-reigning dynasts, like Rupert of the Rhine or August of Saxony, Princes but others give them titles like Count Palatine or Duke. Basically I'm trying to find out what the proper courtesy titles were for the top dynasties, like the Wittelsbachs of Bavaria and the Palatinate, the Welfs of Brunswick and Hanover or the Wettins of Saxony. Any help would be much appreciated!
Beginning in the central Middle Ages, in Germany proper and in the German-culture lands, rule was usually divided between sons, at the exception of the highest degrees of power (kings, electors). So, for instance, all sons of the (Wittelsbach) Duke of Bavaria were Dukes. That did not mean they had always all the same authority. There was usually a kind of land division, such as the ones between Lower and Higher Bavaria (in 1255) or Higher Bavaria, Bavaria-Landshut and Bavaria-Straubing (in 1349).
The senior title, in the Wittelsbach case, the electoral dignity linked to the title of Count Palatine of the Rhine, stayed in the elder line, which explains why the members of this line preferred to use the style "Count Palatine of (their principality)", while being at the same time Dukes of/in Bavaria (and actually holding a good chunk of Bavarian lands). Rupert of the Rhine was, as all other Wittelsbach dynasts, a Count Palatine of the Rhine and a Duke of Bavaria, but, as his family was in dire circumstances, he was never given a principality of his own (otherwise he would be known as Rupert, Count Palatine of Somewhere). He went for a foreign carrier, as did his brothers. In England or in France, titles were not divided between sons, so the all idea of calling a very distant cousin of the actual Duke of Bavaria "Duke Rupert of Bavaria" or the brother of the Elector Palatine "Count Palatine Rupert" seemed odd. It is why Rupert and his brothers were known abroad as "Princes Palatines", something more in touch with the english and french uses.
Same thing went in Brunswick and Saxony, with plenty of Dukes, even if only one Elector at each generation. When the Electors became kings, they changed the house titles alongside the royal examples and all the junior descendants of the kings became princes instead of dukes or counts palatines. Only the remote dynasts kept their "inferior" titles, such as the line of the Dukes in Bavaria - who were nonetheless ranked as princes in the Bavarian court. In Italy, the succession of many ancient dynasties used the same principe : all Pallavicini were marquesses, all Guidi counts. But, as in Germany, the distants dynasts may have not such rank. The only surviving line of Visconti, the Viscounti of Modrone, were separated from the main line before the accession to duchy of Milan, so they had no special title until their own ennoblement.
The western principalities of the Empire, such as Brabant, Lorraine, County of Burgundy, etc never had such a division of power between the sons, so the Lorraine and Savoy dynasts (pretty much the only western principalities to maintain their independence in the early modern era) were not dukes. They were known abroad mainly by their acquired titles (Duke of Guise, Duke of Nemours) but had in France the rank of prince.