264: S-functions Aug 29, 2015

'S' in the English language as a lot of different, and important functions. It forms possessive pronouns such as 'hers', 'ours', and somewhat related, it denotes possession in singular nouns, as well as in plural nouns not having a final '-s'. This use started from the Old English '-es', which was the masculine and neuter genitive singular ending, and now the apostrophe in something such as 'Mary's...' stands in place of an '-e-'. 'S' is also used in conjugating the third person singular of the present of verbs, which originates from the Old English way to conjugate verbs of the same person, number, and tense. 'S' also denotes the plurals of some nouns. This is due to the Old English plural ending '-as'.
For more on genitive endings, see this.