the tie belonging to Mr. Smith = Mr. Smith's tie<br>
the tie belonging to Mr. Smith = Mr. Smith's tie<br>
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However, when it comes to proper nouns that end in an "s" or a "z" sound, it is preferred, although not required, to have the second "s" added in possessive form.
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However, when it comes to [[proper noun|proper nouns]] that end in an "s" or a "z" sound, it is preferred, although not required, to have the second "s" added in possessive form.