Possessives seem like they should be terribly simple to use and understand. Somehow, though, when the writing is in progress, the basic rules that we all know end up riddled with holes from all of the questions that we hurl at them.
Rest assured, however, that unlike some of the evolving rules of spelling and grammar, the rules for possessives are about as simple now as they ever have been in the history of the English language.
A Little History
English was originally inflected, much like Latin. The number, gender, and case of a noun or pronoun could be determined by looking at the ending of the word. In Old English, a noun could have one of four possible cases: nominative, genitive, dative, or accusative. Of these, the genitive case was possessive.
One could typically identify a genitive masculine or neuter noun by its -es ending. However, there were many exceptions to this rule, which complicated matters considerably. For example, distinctions were made between “weak” and “strong” nouns depending on their grammatical role in the sentence.
As Middle English evolved, inflections grew much simpler. An -es ending always marked a genitive noun—at first. However, the reason that inflections were growing simple was that they were actually on their way out. Middle English gradually transformed into Modern English around the 16th century, and grammar and pronunciation changed with it. One example of this change was the introduction of the silent e. In Middle English, the e was always pronounced, giving words such as large and looked two distinct syllables. In Modern English, these became words of one syllable, each having a silent e. The possessive ending -es was now pronounced the same as -s.
Beginning in the 1500s, printers introduced a variation on the genitive -es. Since the e was silent, and arguably extraneous, they borrowed a trick from the French and used an apostrophe to replace the silent letter. The new possessive form was -’s. This practice was optional at first, but by the 1700s it was accepted as standard.
A faulty account of the origin of the -’s form later arose, suggesting that the apostrophe replaced part of the word his. This idea probably came from an alternative possessive form that was once used, in which a possessive pronoun followed a noun; for example, Tom his shoes. The erroneous theory stated that Tom’s is a contraction of Tom and his. Linguists have long known, however, that the Old English -es inflection was the true origin of the current possessive form.
Next up: Basic Rules
Background from Common Errors in English Usage.
The Curious Case of the Evolving Apostrophe
How the apostrophe is still evolving today from MIT Technology Review.
An Introduction to Middle English
Explains how the words were pronounced.