The word 'my' — the first-person singular possessive determiner — descends from Old English 'min' (my, mine), from Proto-Germanic *minaz (my, mine), from PIE *h₁mey-no- or *h₁mene- (of me, belonging to me), a possessive formation built on the oblique pronoun stem *h₁me- (me).
In Old English, 'min' served both the attributive function ('min hus' = my house) and the predicative function ('hit is min' = it is mine). There was no distinction between 'my' and 'mine' — the single form 'min' covered both uses. The split began in Middle English, following a phonological pattern: before consonants, the final '-n' was dropped and the vowel shortened in unstressed speech, producing 'mi' or 'my.' Before vowels, the
This distribution — shorter form before consonants, longer form before vowels — is exactly parallel to the 'a/an' alternation ('a book' but 'an apple'), which developed through the same phonological process at roughly the same time. Both represent the loss of a final nasal consonant before other consonants, with preservation before vowels.
Over time, 'my' generalized as the attributive form regardless of the following sound ('my eyes' replacing 'mine eyes'), and 'mine' was restricted to predicative position ('the book is mine') and absolute use ('mine is better'). By the seventeenth century, the modern distribution was essentially established, though poets continued to use 'mine' before vowels for archaic or elevated effect.
The cognates across Germanic are transparent: German 'mein' (my, mine), Dutch 'mijn' (my, mine), Swedish 'min' (my, mine), Icelandic 'minn' (my, mine). The Latin cognate 'meus' (my, mine) shows the same PIE possessive formation with a different suffix. Greek 'emos' (my) and Sanskrit 'mama' (my, of me) represent alternative possessive formations from the same pronominal root.
The history of 'my' illustrates a general principle of English phonological development: unstressed function words erode faster than stressed content words. 'My' is shorter than 'mine' because it is almost always unstressed in running speech. The possessive determiner ('my book') is a clitic — it leans on the following noun and receives minimal stress. This prosodic weakness drove the shortening from 'min' to 'my,' just as it drove the shortening of 'him' to unstressed ''im,' 'them' to ''em,' and