Vowel /ʊ/ phoneme (short vowel)

The vowel /ʊ/ is the short or lax vowel as in words like hook. Positionally, it is a back high vowel, which occurs in a few other languages. The correct International Phonetic Alphabet (IPA) symbol /ʊ/, i.e. a so-called horseshoe u. Learners may confuse it with the long high back vowel /u/ as in cool or flute. The difference between /ʊ/ and /u/ is not primarily length, but the fact that /ʊ/ is a lax vowel while /u/ is tense. In this article, slash marks like /ʊ/ indicate a phoneme, while angled brackets like <ʊ> indicate a letter or spelling, and square brackets like [ʊ] indicate a precise phonetic transcription, e.g. indicating a phonetic variant of a sound.

1 Linguistic description

The vowel /ʊ/ is not just a shortened version of /u/, but it is a qualitatively different vowel altogether.

It is a high back vowel, meaning that the back of the tongueis relatively high in the mouth, near the position for /u/, and thus the locus of the vowel is the back of the tongue and mouth. More precisely, it is a near-close and near-high vowel, while the long vowel /u/ as in flute is the true and fully high and fully back vowel.
In English /ʊ/ is a short vowel, while /u/ is long. However, the crucial difference between /ʊ/ and /u/ is that /i/ is tense, while /ʊ/ is lax, so /ʊ/ is primarily a lax vowel. The tongue is essentially a muscle, and for /u/ it tenses, making the tongue blade and tip fully high and front, and making the vowel longer in duration. For /ʊ/ the tongue muscle is relaxed, making the vowel shorter. The laxness also affects the tongue position, so that the tongue is not raised as high and is not as far back in the mouth as for /u/. Thus, the tongue is positioned not quite as high or forward as /u/; the vowel is slightly lowered and centralized (drawn somewhat toward the center of the mouth) for /ʊ/.
The vowel /ʊ/ is rounded, i.e., the lips are somewhat rounded (though this is less of a concern for most teachers, as the upper back vowels in English are all rounded, and tend to be unrounded by default in other languages).

As a vowel, the glottis (vocal cords) vibrate, producing a fundamental frequency (F0), which provides the basic intonation of the voice, particularly the vowels and voiced consonants. As the F0 bounces around the vocal cavity, other harmonic frequencies are produced, including the so-called F1 and F2, which are responsible for primary vowel quality.

Until 1989, the IPA allowed for an alternate symbol for this sound, the symbol <ɷ>, which is no longer an IPA symbol, though a few texts may still use it. Another older symbol, especially used by American linguists, was <ᴜ>, a small capital U without the tail. Both symbols may still be used in some texts and dictionaries.

1.1 Cross-linguistic comparison

This vowel is much less common in the world's languages, as the tense vowel /u/ tends to predominate cross-linguistically. It is found as a phoneme in German (e.g., Stunde), but otherwise, it is fairly rare across the world's languages. This sound or very similar vowels may occur as allophones or regular sounds in some dialects of European and other languages. This sound can pose difficulty for learners who lack this vowel.

Korean and Japanese have /u/, and also have a different vowel: an unrounded back vowel, which is like /ʊ/ or /u/, but with the lips completely spread or unrounded, represented by the IPA symbol /ɯ/. They may pronounce this instead of /ʊ/, e.g., in the Korean / Japanese accented pronunciation of good as [gɯd]<ref>In Japanese, at least in romanization of Japanese, /ɯ/ is spelled <-u-> as in Fuji, while /u/ is spelled <-ou->. In Korean, the letter 으 spells /ʊ/, romanized as u or ŭ, and 우 spells /u/, romanized variously as u, uw, woo, wu.

1.2 Teaching /ʊ/ production

Again, it is important for teachers and learners to realize that /ʊ/ is not just a shortened version of /u/, but it is a qualitatively different vowel altogether, as the tongue tensing and position are different. The main distinction has to do with muscular tenseness in the tongue; the long vowel is actually tensed, while the short vowel is relaxed, which slightly alters the tongue position; for the lax vowel, the tongue is slightly lower and not so strongly back or high in the mouth. Students from an L1 without this vowel will confuse it with /u/ in their listening and pronunciation.

However, /ʊ/ is not so common in English, and there are not so many minimal pair words where the /ʊ/ - /u/ contrast makes a difference in meaning. The difference between the lax vowel /ɪ/ versus the tense or long vowel /i/ is much more important, i.e., the bit vowel versus the beat vowel. The /ɪ/ - /i/ distinction is more important in English, as there are many more English words with /ɪ/, and many word pairs like bit / beat where there potential problems could arise by not pronouncing the lax vowel /ɪ/ or the /ɪ/ - /i/ distinction correctly. Thus, the /ʊ/ sound and the /ʊ/ - /u/ distinction are less of a priority than other vowel phonemes.

In teaching to produce it, students should not just learn to clip the long /u/ vowel short. They need to learn to relax the tongue to modify the tongue position. One could have students to pretend that the tongue is numb, e.g., due to cold weather, or from having had an anesthetic shot or medication for the tongue from a dentist. Koreans and Japanese may say /ɯ/ instead of /ʊ/, and need to practice rounding their lips and relaxing the tongue. Perhaps they can practice starting with sating /ɯ/ and then relaxing the tongue and rounding the lips.

Some dictionaries and learner materials can cause confusion. The long vowel /u/ can also be indicated with a colon to specify the long vowel, as in /u:/; this may be helpful for learners, but this is not really necessary for English, as the /u/ sound is naturally longer and tensed. Because /u/ is long and tensed, it has a slight off-glide, and may also be written as /uw/ in some texts. The lax vowel should not be indicated with /u/ as some dictionaries do, such as those published in Korea, where the lax vowel is written incorrectly as /u/ and the tensed vowel as /u:/; this can confuse learners.

2 Lax /ʊ/ versus tense /u/

The primary difference between these two vowels is the tense/lax distinction, not the long/short distinction. The /ʊ/ is shorter because it the tongue muscle is lax. The laxing gives the /ʊ/ a qualitatively different vowel quality from /u/, so /ʊ/ is not a shortened or clipped version of /u/, but an essentially different vowel phoneme. The vowel /ʊ/ also contrasts with the short lax vowel /ʌ/ as in luck; this vowel is produced around the center of the mouth over the central part of the tongue, and it is known as a central mid vowel.

The vowel /ʊ/ never occurs in word-initial position, and rarely in final position. It mainly occurs medially, that is, in the middle of words. The lax vowel /ʊ/ started to develop in English after other vowels had undergone massive changes, known as the Great Vowel Shift, in the 16th and 17th centuries. After the other vowels had undergone changes such as diphthongization and changes in vowel quality, the tense vowel /u/ then started to shorten and centralize to /ʊ/, but this change abruptly stopped for reasons that are unclear. The shortening of /u/ was incomplete, and only affected /u/ in some words in certain phonemic contexts. It primarily affected <-ook> as in book, but not all <-ook> words, and it affected some words in other types of syllables or words, e.g., some <-ood>, <-oot> and a few <-u-> words.

2.1 Occurrence

The vowel /ʊ/ tends to occur in the following types of words or positional contexts. It is most often spelled <-oo->, and sometimes <-u->, especially in older English words that underwent the partial /ʊ/ vowel shift.

2.1.1 Before <k, d, t>

The letter <-u-> is pronounced /ʊ/ before the letters <k, d, t, l> in some older words, but not always; it is sometimes pronounced /u/ or /ʌ/.

spelling	lax /ʊ/	tense /u/	lax /ʌ/
<k>	book, brook, cook, crook, hook, look, nook, rook, shook, schnook forsook, took, betook, partook, mistook, wookie	gobblygook, kook, spook
<d>	wood, stood, hood, good	brood, food, mood, rood	blood, flood
<t>	foot, afoot, barefoot, soot, root^†	boot, coot, hoot, loot, moot, root, shoot, toot bandicoot, cahoots, reboot, uproot
<l>	wool	cool, drool, pool, fool

† Note: A few words like root are variable, depending on region; it can be tense or lax. The following words are usually pronounced with tense /u/, but it can become lax in some regional American dialects.

Before <l>: cool, pool, stool, fool, school, drool, spool, tool
Before <m>: room, broom, groom

2.1.2 The letter <-u-> in some words

cushion, push, put, pull, full, bull, sugar, sure

2.1.3 The sequence <wo-> and similar spellings

This group consists of a very small number of words.

wolf, Worcester, wolfram, wolframite, wool, wood, wolverine, wookie, woof, woops, whoop, whooping

2.1.4 The sequence <ou> in modal verbs

would, wouldn’t, could, couldn’t, should, shouldn’t

2.1.5 In reduced function words

In weak, unstressed forms of one-syllable words, /u/ in an unstressed word reduces to /ʊ/ in colloquial English. Some function words can reduce further to the schwa vowel /ə/ as in about or the (/ə/ is very similar to /ʌ/, but extra-short, occurring only in unstressed syllables).

Function word	Careful enunciation		Colloquial		Fast speech
to	[tu]	→	[tʊ]	→	[tə]
who	[hu]	→	[hʊ]
who’d	[hud]	→	[hʊd]
you	[yu]	→	[yʊ]	→	[yə]
you’d	[yud]	→	[yʊ]
do	[du]	→	[dʊ]

3 Practice materials and activities

Minimal pairs, which contrast a target sound with a sound that is a separate phoneme, are typical starting points for production and practice activities, particularly comparing /ɪ/ and /i/. These sounds can be contrasted with each other in minimal pair contrasts in syllable-initial or word-initial position, and in medial position (middle of a word). The lax vowel does not generally occur in word-final position. For more on types of minimal pairs activities to train listeners to discern and produce sounds, see the following.

3.1 Minimal pair contrasts

The tense and lax vowels /u/ and /ʊ/ contrast in only a few pairs of words, since this lax vowel is not so common in English.

/ʊ/	/u/
could full hood looker look pull should soot wood	cooed fool who’d lucre Luke pool shooed suit wooed

The lax vowel /ʊ/ contrasts with the lax vowel /ʌ/ in a few words; the /ʌ/ is a short, lax vowel, slightly lower than /u/ or /ʊ/, and with the lips unrounded.