I was taught that the apostrophe replaces a missing letter - so Mark's book is the abbreviated form of the older English 'Mark, his book' and so on. Therefore it would be incorrect to put it in if you mean more than one Mark - just as it would be if you were talking about the unit of currency - more than one Bosnian mark, or the since replaced Deutschmark, is always written "marks".
More than one Louis however has the problem that words ending in 's' would normally be pluralised using 'es' - buses, asses, etc - except that more than one Louis would then be Louises and so the normal form of pluralising will change the gender. In that case it might be reasonable to replace that 'e' with an apostrophe so that you get Louis's - and so to then denote something (say a pen) as the possession of a single Louis you would replace the 'his' completely so making "Louis' pen".
See? Simples! To quote Aleksandr Orlov of Compare the Meerkat dot com! (Aleksandr Orlov is the most loved person in British advertising, and would doubtless be the next Prime Minister if he stood for Parliament... it's hard to explain but if you've never come across the Compare the Market ads you must go to look!)
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Date: 2010-04-16 11:43 am (UTC)More than one Louis however has the problem that words ending in 's' would normally be pluralised using 'es' - buses, asses, etc - except that more than one Louis would then be Louises and so the normal form of pluralising will change the gender. In that case it might be reasonable to replace that 'e' with an apostrophe so that you get Louis's - and so to then denote something (say a pen) as the possession of a single Louis you would replace the 'his' completely so making "Louis' pen".
See? Simples! To quote Aleksandr Orlov of Compare the Meerkat dot com! (Aleksandr Orlov is the most loved person in British advertising, and would doubtless be the next Prime Minister if he stood for Parliament... it's hard to explain but if you've never come across the Compare the Market ads you must go to look!)