no

The word 'no' is the primary negation word in English, but its apparent simplicity conceals a double etymology.‍​‌​‌​‍​‌​‌​‌​‍​‍​‌​‍​‍​‌​‍​‍​‍​‍​‍​‍​‍​‍​‌​‍​‌​‍​‍​‍​‍​‍​‍​‍​‌ Modern English 'no' actually represents the merger of two distinct Old English words: the adverb 'nā' (no, not, never) and the determiner 'nān' (no, none, not one). Both were built from the Proto-Germanic negator *nē, which descends from PIE *ne (not), but they were formed differently and originally served different functions.

The adverb 'nā' — used to negate a statement or refuse a request ('No, I will not') — is a contraction of Old English 'ne' (not) + 'ā' (ever, always), literally 'not ever.' This is the 'no' of refusal, the word speakers use to reject, deny, or contradict. The determiner 'nān' — used to negate a noun ('no man,' 'no reason') — is a contraction of 'ne' (not) + 'ān' (one), literally 'not one.' From 'nān' also descend 'none' (not one) and 'nothing' (not a thing). During the Middle English period, both forms shortened to 'no,' and the distinction between the adverbial and determiner uses became a matter of syntax rather than form.

The PIE root *ne is perhaps the most fundamental grammatical root in the entire family, as it provided the negation system for virtually every daughter language. Its reflexes include Latin 'ne' (not, lest), 'nihil' (nothing — ne + hilum, not a thread), 'nullus' (none — ne + ullus, not any), 'nec/neque' (and not, neither), and the prefix 'in-' (not, as in 'invisible,' 'impossible'). Greek 'nē-' produced 'nēpenthēs' (without grief — giving English 'nepenthe'). Sanskrit 'na' (not) is the direct cognate. The Germanic branch built an extensive negative vocabulary from *nē: 'not' (from 'nā + wiht,' not a thing), 'never' (ne + ever), 'neither' (ne + either), 'nor' (ne + or), 'nowhere' (ne + where), 'naught' (ne + ought/aught, not anything).

The history of English negation is a story of cycles. Old English used double or multiple negation as standard grammar: 'ic ne seah nān þing' (I not saw no thing) was emphatic, not redundant. During the Middle English period, this system gradually weakened, and by the Early Modern English period, prescriptive grammarians — influenced by Latin logic — began to condemn double negation as illogical. The modern standard-English rule that two negatives make a positive is a relatively recent imposition, not an ancient feature of the language. Many English dialects worldwide continue to use multiple negation in the Old English pattern.

The pronunciation of 'no' as /nəʊ/ (with a diphthong) reflects the Great Vowel Shift. Old English 'nā' had a long monophthong /aː/, which Middle English preserved, and the Great Vowel Shift (c. 1400–1700) raised and diphthongized to /noː/ and eventually /nəʊ/. The same shift affected 'so,' 'go,' 'know,' and other words with historical long 'a' or 'o.'