How to pronounce -on endings?

To reduce or not to reduce?

You’ve asked whether there’s any rhyme or reason to how we pronounce a word ending in -on. There is, yes, a bit of that here and there. Mostly it’s about stress.

First let’s look at a bunch of such words to see what patterns pop out. I’ve sorted these words back to front to help make any patterns more apparent. The key is explained below, but in short the bold words are not reduced, the italic words might be reduced, and the rest of them are reduced to a schwa.

kaon, gibbon, ribbon, ebon, carbon, Bourbon, Lisbon, con, bacon, beacon, deacon, recon, icon, Rubicon, Helicon, silicon, catholicon, salpicon, Horicon, lexicon, falcon, neo-con, air-con, retcon, don, head-on, radon, mastadon, add-on, gladdon, myrmidon, abandon, tendon, London, codon, pteranodon, iguanodon, dimetrodon, glyptodon, hard-on, pardon, udon, Croydon, eon, aeon, paeon, dudgeon, gudgeon, curmudgeon, pigeon, wigeon, dungeon, habergeon, burgeon, chirurgeon, sturgeon, luncheon, truncheon, escutcheon, pheon, pantheon, Cleon, chameleon, galleon, come-on, neon, peon, thereon, freon, chiffon, griffon, decagon, dodecagon, flagon, paragon, dragon, tetragon, metagon, pentagon, wagon, hexagon, Lake Wobegon, Oregon, tigon, Klingon, trogon, jargon, polygon, cabachon, lechon, siphon, colophon, morphon, Typhon, talkathon, walkathon, swimathon, telethon, python, ion, coercion, scion, contagion, legion, fashion, lion, vermilion, pavilion, medallion, stallion, hellion, billion, million, trillion, zillion, bullion, minion, onion, union, bunion, pion, champion, Hyperion, criterion, Orion, chorion, chlorion, prion, carrion, expression, fission, mission, fusion, nation, election, completion, exertion, contortion, Zion, beckon, Yukon, talon, felon, echelon, melon, mamelon, muskmelon, watermelon, paddymelon, Teflon, mouflon, triathlon, epsilon, upsilon, gallon, reveillon, carillon, buillon, colon, merlon, Babylon, Ceylon, nylon, pylon, cinnamon, c’mon, demon, hegemon, lemon, pentstemon, salmon, backgammon, common, Solomon, sermon, Mormon, ichneumon, etymon, anon, canon, legomenon, phenomenon, xenon, pignon, Agamemnon, cannon, phonon, capon, weapon, crampon, tampon, Nippon, upon, whereupon, coupon, put-upon, Ron, baron, Charon, macron, hadron, squadron, tetrahedron, polyhedron, cauldron, almendron, interferon, heron, cameron, Decameron, saffron, iron, boron, moron, apron, marron, cimarron, turron, patron, electron, citron, positron, intron, cyclotron, cosmotron, neutron, pleuron, pteropleuron, Huron, chevron, chyron, reason, treason, season, mason, meson, bison, Madison, benison, venison, unison, poison, caparison, comparison, grison, orison, prison, imprison, garrison, jettison, vison, crimson, Stevenson, Johnson, arson, parson, Anderson, person, lesson, Watson, baton, hyperbaton, automaton, Eton, Princeton, skeleton, simpleton, Breton, Briton, plankton, Hilton, Stilton, wanton, photon, peloton, lepton, Norton, piston, button, glutton, mutton, futon, crouton, put-on, sexton, phyton, muon, Devon, axon, klaxon, Saxon, taxon, exon, yon, rayon, halcyon, Procyon, tachyon, canyon, pinyon, baryon, carry-on, emblazon, horizon.

This list is by no means meant to be “all” of them—just a sampling of the usual suspects, and some less usual ones as well.

Mark-up Groups

I’ve divided that list up into three mark-up categories:

1. Unmarked words are those whose final -on is “always” reduced.
   
   This is usually to a schwa [ə] and sometimes even more so, such as in cotton where all that’s left is a syllabic consonant, [n̩], doing the work of a vowel there.
2. Bold words are those whose final -on is “never” reduced.
   
   The unreduced vowel at the end either has primary stress or else it may, particularly in America, have secondary stress.
   
   Even though these aren’t reduced, that doesn’t mean that all speakers have the same vowel there, as the exact vowel used varies between speech communities. In the UK this is nearly always the rounded CLOTH vowel, which for them is [ɒ]. In America it is much more often the unrounded FATHER vowel [ɑ] in most speakers, even though a notable minority have the rounded CLOTH vowel there and a few even have the even more rounded THOUGHT vowel—and both CLOTH and THOUGHT usually have [ɔ] in America.
3. Italic words are those whose final -on is “sometimes” reduced.
   
   That means that some accents, and some speakers, leave the vowel unreduced like the group-two words, but others reduce it to a schwa like the group-one words. Sometimes this variability is present in both UK and US speakers alike, but more often it is the UK speakers who reduce the vowel and US speakers who leave it unreduced.
   
   US speakers who do not reduce it have a secondary stress on that final syllable that the UK speakers do not.

Observations

What observations can we make about the patterns we see?

• The UK reduces many more words than the US does.

• The most important factor here is stress. If the final syllable is stressed, as in anon, upon, don, chiffon, it cannot be reduced.

• Compound words ending with a hyphenated preposition on or upon never reduce.

• The reason baton is marked in italic as sometimes being reduced is because its stress switches as you cross the Atlantic: it’s an unreduced /bəˈtɑn/ in the US but only /ˈbætən/ in the UK.

• All the words that have ‑tion, ‑cion, ‑sion where the consonant plus a following i constitute a digraph for phonemic /ʃ/ (occasionally [ʒ]), are reduced.

• All the ‑geon words reduce.

• The longer the word has been around, the more likely it is to reduce.

• Many of the never-reduced words are “new” terms that are mainly seen in technical contexts, which are conservative.

• Loanwords with “foreign” pronunciations quickly naturalize into versions that better follow English sound patterns. As one example, for the French loanword réveillon, in 1982 the OED had only the non-naturalized pronunciation /revɛjɔ̃/, but by the word’s 2010 update, it also lists UK /ˌrɛveɪˈjɒn/, U.S. /ˌrɛveɪˈjɑn/. Given the stress at the end, it can’t reduce further.

• Carrion and carry-on are a minimal pair, where the first is reduced but the second is not. A carry-on bag is luggage you don’t check for your flight but keep close to you. A carrion bag might be one that holds dead critters. You probably shouldn’t attempt to use a carrion bag as a carry-on bag. :)

• A come-on and the eye-dialect spelling c’mon are also a minimal pair, but only in stress: neither reduces. The first is stressed at the start, the second at the rear.

Surprises, surprises

For the words from the third set, speakers who have never heard the other version will often be surprised by it, since they never imagined anyone would do it differently than they do. Because of media exposure, this is more often US speakers who are surprised by UK pronunciations than the other way around.

This reduction of unstressed syllables is a common feature of UK English that’s seen in other contexts as well, such as in secretary or medicine. The UK versions seem shorter to us Americans, more worn-down by use and time perhaps.

But not always. Consider Lake Wobegon, Horicon, Oregon. The first one won’t reduce because it’s transparently derived from woe begone. The other two are, among other things, names of places in southern Wisconsin. In that accent, neither word reduces—and in fact, Horicon and Oregon sound rather similar at some level.

However, for speakers living in the actual US state of Oregon, that word does reduce there, possibly even to the point of making it homophonous with organ. This caused light, humorous friction when Garrison Keillor took his Lake Wobegon road-show to that state, since he naturally pronounces their city’s name differently in his accent than they do in theirs.

So that’s not a US–UK difference; it’s a difference within the United States itself. When one teaches schoolchildren in Wisconsin and Minnesota about the Oregon Trail, that first word does not reduce there.

Misfits

There are a few more minor categories I haven’t covered yet, as there are only a few words in each group:

4. Monosyllabic words with the CUT vowel [ʌ]: won, son, ton, hon. Given that [ʌ] is just the way we write [ə] when it’s stressed, perhaps one might argue that this also counts as a reduction, but I’ll leave that task to others.

5. Imported words from Romance (mostly Spanish) that have retained the original GOAT vowel, [o]: garçon, soupçon, chaperon, rincon, reggaeton, chicharron, bodegon, maricon, melocoton, diallelon. The last syllable held a monophthong in the original languages; it remains so only in those English dialects that still have a monophthongal [o], including Scotland and the northern parts of the US both east and west. Other accents have a non-phonemic, very slight phonetic diphthong that’s often written [oʊ]. Fully assimilated words from Spanish that there ended in a stressed ‑ón become ‑oon in English, thus switching their vowel from /o/ to /u/, as in doubloon, picaroon, quadroon.

6. I am not counting words that end in ‑oon like moon, noon, buffoon, cocoon, cartoon, afternoon, lagoon, baloon, baboon — because those always have stressed /u/ and never reduce.

See also Why do photons and protons exhibit such anomalous behavior?.