/wɪtʃ/
[pronoun] Used to ask about or identify one or more things from a group, or to give more information about something already mentioned. For example, you use it to ask 'which one do you want?' or to say 'the book which I borrowed was excellent.'
'Which' originally meant 'of what kind of person' — it once referred to people, not just things.
The word 'which' stretches back to the very foundations of the English language, emerging from Proto-Germanic *hwilīkaz, a compound meaning roughly 'of what form' or 'of what kind.' This ancient root was made of two parts: *hwi-, the interrogative stem meaning 'what' or 'who,' and *līkaz, meaning 'body,' 'form,' or 'appearance' — the same root that gives us the modern English word 'like' in the sense of resemblance. So at its deepest origin, 'which' asked not just 'what thing?' but 'what body?' or 'what shape of being?'
In Old English, this became hwilc or hwylc, pronounced with a strong initial 'hw' sound that was fully articulated in Anglo-Saxon speech — something like 'hwilch.' This Old English form was used to ask about both people and things, and it could mean something close to 'what sort of person' or 'what manner of thing.' The medieval mind did not yet draw a firm line between 'which' for objects and 'who' for people; both roles overlapped freely in early usage, and you could quite naturally ask hwilc man — 'which man' — in a sentence where modern English would use 'who.'
As the Middle English period arrived, roughly from the 11th to 15th centuries, hwylc softened and shifted. The initial 'hw' gradually simplified in many dialects to a plain 'w' sound, and the spelling settled toward 'which,' though medieval manuscripts show delightful variation: whiche, whych, qwhilk, and quilk all appear in different regional texts. The northern English and Scottish dialects held onto the older 'wh' pronunciation — and even the full 'hw' — for far longer than southern dialects, and Scottish English today still sometimes reflects this ancient distinction.
Around the 14th and 15th centuries, a quiet but important shift began: 'which' started to be preferred for things and animals, while 'who' and 'whom' increasingly took over for people. This was not a sudden rule imposed by grammarians but a slow, natural drift in everyday speech. Chaucer uses 'which' for people without any sense of oddness, and the King James Bible of 1611 famously retains 'which' in the Lord's Prayer — 'Our Father, which art in heaven' — a construction that today sounds archaic precisely because this boundary between 'which' and 'who' had not yet hardened when that translation was made.
The debate that grammarians love — 'which' versus 'that' in relative clauses — is largely a modern invention. For most of English history, the two words were used interchangeably to introduce a clause describing a noun. It was not until the late 19th and early 20th centuries that prescriptive grammarians, particularly in American English, began insisting that 'that' should be used for essential clauses ('the book that I lost') and 'which' for non-essential ones ('the book, which I found later, was damaged'). British English has never fully adopted this rule, and it remains one of the most debated points of style in the English-speaking world — all because of a pronoun that once simply asked, in the oldest Germanic tongue, 'of what kind of body are you?'