How English evolved to give us two indefinite articles ("a" and "an") and the odd mix of possessive pronouns that don't quite match.
The Oxford English Dictionary says that the loss of “n” happened over the course of three centuries, starting in the 12th century. The change was so thorough that it even happened before words beginning with a vowel. In other words, for a while, speakers were saying “a apple” instead of “an apple” before things settled down into the situation of Standard English today. Some speakers still do use “a” even before vowels, but these days it’s regarded as nonstandard.
As a side note, ever since the consonants-versus-vowels rule come to be standard, there has always been variation in whether to use “a” or “an” before words that begin with “h,” especially when that “h” is at the front of an unstressed syllable, where it is prone to disappear. You can hear more about “an” before words such as “historic” in episode 261.
“My” and “Thy” Came From “Mine” and “Thine”
Just as “a” developed from the older form, “an,” the forms “my” and “thy” developed from the older forms “mine” and “thine.” “Mine” started losing its final “n” before a consonant at about the same time as “an” did, in the 12th century. In the following century, so did “thine.”
But for whatever reason, even though we still have the two forms “a” and “an,” the forms “mine” and “thine” as possessive pronouns have fallen by the wayside. The Oxford English Dictionary has examples of “my” and “thy” coming before words that began with a vowel in the early 15th century, and they had finally taken over as the standard forms by the end of the 1700s. Or at least, “my” did. “Thy” did somewhat, only to be replaced by “your” later, which we discussed in episode 369 about “I” taking what seems like a plural verb.
“Mine” Is Still Used for “My” in Some Situations
There are a few exceptions in which “mine” is still used as a possessive pronoun, though. You’ll sometimes find it in poetry or song lyrics; for example, “The Battle Hymn of the Republic,” written in 1861, begins with the line “Mine eyes have seen the glory of the coming of the Lord.” Notice that “eyes” begins with a vowel. Also, if you want to put the possessive pronoun after a noun for stylistic effect, you’ll use “mine.” Walt Disney did this in the movie Dumbo, in the song “Baby Mine.”
But before “mine” and “thine” fell out of favor, they were enough of a team that they made some ripples in the pond for the rest of the possessive pronouns. That final “n” for “mine” and “thine” was enough of a recognizable pattern that a process of analogy kicked in, and people started putting a final “n” on the other possessives, giving us “hisn,” “hern,” “ourn,” “yourn,” and “theirn.” According to the American Heritage Dictionary, these final-“n” forms date back to Middle English, but exist these days only as regional forms. As far as I know, there was never an “itsn” form of “its,” but that’s not surprising, since “its” only joined the ranks of possessive pronouns at the beginning of the Modern English period. Before then, speakers just used “his.”