An apostrophe stands for a missing letter or letters. In old English, the genetive case was formed by adding -es to the end of a word: "the book of Mark" would be written as "Markes book". Modern English misses out the 'e' sound, and so the word is shortened to Mark's instead of Markes.
As such, I never include an apostrophe to mark a plural. Not only is it, I submit, incorrect, it's also confusing because it can be mistaken for a possessive. (I'm generally a descriptivist, not a prescriptivist, when it comes to grammar; but something can still be "wrong" in a language if it prevents people communicating their meanings effectively.)
So: 80s not 80's The As and the Bs, not the A's and the B's.
I would write the plural of Louis (French pronunciation, /'lu:ɪ/) as Louis (pronounced /'lu:ɪz/), although for clarity I might reword the sentence to make it clear it's a plural. If you pronounced it as an English name, sounding the final 's' in the singular, then the plural would be 'Louises' - but because that sounds like the plural of the girl's name Louise, I'd probably try to reword the sentence.
Technically, I'd say the plural of "buffy" would be "buffies", but when it's a proper name I'd pluralise Buffy as Buffys, just because that feels more respectful.
The plural of King Henry is King Henrys, because 'Henry' is a proper noun, not an adjective. While it's fun to pluralise expressions like 'Lords Appellant' or 'Courts Martial' or 'Advocates General', those are simply a case of putting the adjective after the noun instead of before it in imitation of mediaeval French practice. A court martial is a martial court, an advocate general is a general advocate; but king Henry isn't a henry king. :-)
I tend to add 's to proper names ending in -s to denote the possessive, because thaty's also how I pronounce them. Giles's book, because I'd pronounce that /'dʒaɪlzəz 'bʊk/ not /'dʒaɪlz 'bʊk/.
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An apostrophe stands for a missing letter or letters. In old English, the genetive case was formed by adding -es to the end of a word: "the book of Mark" would be written as "Markes book". Modern English misses out the 'e' sound, and so the word is shortened to Mark's instead of Markes.
As such, I never include an apostrophe to mark a plural. Not only is it, I submit, incorrect, it's also confusing because it can be mistaken for a possessive. (I'm generally a descriptivist, not a prescriptivist, when it comes to grammar; but something can still be "wrong" in a language if it prevents people communicating their meanings effectively.)
So:
80s not 80's
The As and the Bs, not the A's and the B's.
I would write the plural of Louis (French pronunciation, /'lu:ɪ/) as Louis (pronounced /'lu:ɪz/), although for clarity I might reword the sentence to make it clear it's a plural. If you pronounced it as an English name, sounding the final 's' in the singular, then the plural would be 'Louises' - but because that sounds like the plural of the girl's name Louise, I'd probably try to reword the sentence.
Technically, I'd say the plural of "buffy" would be "buffies", but when it's a proper name I'd pluralise Buffy as Buffys, just because that feels more respectful.
The plural of King Henry is King Henrys, because 'Henry' is a proper noun, not an adjective. While it's fun to pluralise expressions like 'Lords Appellant' or 'Courts Martial' or 'Advocates General', those are simply a case of putting the adjective after the noun instead of before it in imitation of mediaeval French practice. A court martial is a martial court, an advocate general is a general advocate; but king Henry isn't a henry king. :-)
I tend to add 's to proper names ending in -s to denote the possessive, because thaty's also how I pronounce them. Giles's book, because I'd pronounce that /'dʒaɪlzəz 'bʊk/ not /'dʒaɪlz 'bʊk/.