In English, the digraph ⟨th⟩ represents in most cases one of two different phonemes: the voiced dental fricative /ð/ (as in this) and the voiceless dental fricative /θ/ (thing). More rarely, it can stand for /t/ (Thailand, Thames) or, in some dialects, even the cluster /tθ/ (eighth). It can also be a sequence rather than a digraph, as in the /t.h/ of lighthouse.
In standard English, the phonetic realization of the dental fricative phonemes shows less variation than for many other English consonants. Both are pronounced either interdentally, with the blade of the tongue resting against the lower part of the back of the upper teeth and the tip protruding slightly or alternatively with the tip of the tongue against the back of the upper teeth. The interdental position might also be described as "apico-" or "lamino-dental". These two positions may be free variants, but for some speakers they are complementary allophones, the position behind the teeth being used when the dental fricative stands in proximity to an alveolar fricative /s, z/, as in clothes (/ðz/) or myths (/θs/). Lip configuration may vary depending on phonetic context. The vocal folds are abducted. The velopharyngeal port is closed. Air forced between tongue surface and cutting edge of the upper teeth (interdental) or inside surface of the teeth (dental) creates audible frictional turbulence.
The difference between /θ/ and /ð/ is normally described as a voiceless-voiced contrast, as this is the aspect native speakers are most aware of. However, the two phonemes are also distinguished by other phonetic markers. There is a difference of energy (see: Fortis and lenis), the fortis /θ/ being pronounced with more muscular tension than the lenis /ð/. Also, /θ/ is more strongly aspirated than /ð/, as can be demonstrated by holding a hand a few centimeters in front of the mouth and noticing the differing force of the puff of air created by the articulatory process.
As with many English consonants, a process of assimilation can result in the substitution of other speech sounds in certain phonetic environments. Native speakers do this subconsciously.
At the word boundaries alveolar stops next to dental fricatives assimilate very regularly, especially in rapid colloquial speech, involving both the place of articulation and the manner of articulation: the alveolar stops become dental, while the dental fricatives become stops. The resulting consonant is usually long (geminated) which may be the only cue for the speaker to distinguish particular words (for example, the definite and indefinite articles, compare "run the mile" [-n̪n̪ə-] and "run a mile" [-nə-]).
- in the: /n‿ð/ → [n̪n̪]
- join the army: /n‿ð/ → [n̪n̪]
- read these: /d‿ð/ → [d̪d̪]
- right there, get them: /t‿ð/ → [t̪t̪]
- fail the test: /l‿ð/ → [l̪l̪]
- till they: /l‿ð/ → [l̪l̪]
The alveolar sibilants may become dental as well:
- this thing: /s‿θ/ → [s̪θ] or [s̪s̪]
- takes them: /s‿ð/ → [s̪ð] or [s̪s̪]
- was them: /z‿ð/ → [z̪ð] or [z̪z̪]
/θ/ and /ð/ can also be lost through elision: months [mʌns], clothes [kloʊz]. In rapid speech, sixth(s) may be pronounced like six. Them may be contracted to 'em, and in this case the contraction is often indicated in writing.
In some areas, such as London and northern New Zealand, and in some dialects, including African American Vernacular English, many people realise the phonemes /θ/ and /ð/ as [f] and [v], respectively. Although traditionally stigmatised as typical of a Cockney accent, this pronunciation is fairly widespread, especially when immediately surrounded by other fricatives for ease of pronunciation, and has recently been an increasingly noticeable feature of the Estuary English accent of South East England. It has in at least one case been transferred into standard English as a neologism: a bovver boy is a thug, a "boy" who likes "bother" (fights). Joe Brown and his Bruvvers was a Pop group of the 1960s. The song "Fings ain't wot they used t'be" was the title song of a 1959 Cockney comedy. Similarly, a New Zealander from the northernmost parts of the country might state that he or she is from "Norfland".
Note that, at least in Cockney, a word beginning with /ð/ (as opposed to its voiceless counterpart /θ/) can never be labiodental. Instead, it is realized as any of [ð, ð̞, d, l, ʔ], or is dropped altogether.
Many speakers of African American Vernacular English, Caribbean English, Liberian English, Nigerian English, Philadelphia English, and Philippine English (along with other Asian English varieties) pronounce the fricatives /θ, ð/ as alveolar stops [t, d]. Similarly, but still distinctly, many speakers of New York City English, Chicago English, Boston English, Indian English, Newfoundland English, and Hiberno-English use the dental stops [t̪, d̪] (typically distinct from alveolar [t, d]) instead of, or in free variation with, [θ, ð].
It is often parodied as ubiquitous to French- and German-speaking learners of English, but is widespread among many other foreign learners of English, because the dental fricative "th" sounds are not very common among world languages.
|/s, z/||/θ, ð/||IPA||Notes|
|bass||bath||ˈbæs||bass in the sense of a kind of fish.|
|soar||thaw||ˈsɔː||Non-rhotic acents with horse-hoarse merger.|
|soar||Thor||ˈsɔː(r)||With horse-hoarse merger.|
|soared||thawed||ˈsɔːd||Non-rhotic acents with horse-hoarse merger.|
|sore||thaw||ˈsɔː||Non-rhotic acents with horse-hoarse merger.|
|sore||Thor||ˈsɔː(r)||With horse-hoarse merger.|
|sored||thawed||ˈsɔːd||Non-rhotic acents with horse-hoarse merger.|
|sword||thawed||��sɔːd||Non-rhotic acents with horse-hoarse merger.|
|whiz||with||ˈwɪz||With wine-whine merger.|
In many varieties of Scottish English, /θ/ becomes [h] word initially and intervocalically. It is a stage in the process of lenition, and is how th is normally pronounced syllable-initially in Gaelic.
Th-debuccalization occurs mainly in Glasgow and across the Central Belt. A common example is [hɪŋk] for think. This feature is becoming more common in these places over time, but is still variable. In word final position, [θ] is used, as in standard English.
The existence of local [h] for /θ/ in Glasgow complicates the process of th-fronting there, a process which gives [f] for historical /θ/. Unlike in the other dialects with th-fronting, where [f] solely varies with [θ], in Glasgow, the introduction of th-fronting there creates a three-way variant system of [h], [f] and [θ].
Use of [θ] marks the local educated norms (the regional standard), while use of [h] and [f] instead mark the local non-standard norms. [h] is well known in Glasgow as a vernacular variant of /θ/ when it occurs at the start of a word and intervocalically, while [f] has only recently risen above the level of social consciousness.
Given that th-fronting is a relatively recent innovation in Glasgow, it was expected that linguists might find evidence for lexical diffusion for [f] and the results found from Glaswegian speakers confirm this. The existing and particular lexical distribution of th-debuccalization imposes special constraints on the progress of th-fronting in Glasgow.
In accents with th-debuccalization, the cluster /θr/ becomes [hr], giving these dialects a consonant cluster that doesn't occur in other dialects. The replacement of /θr/ with [hr] leads to pronunciations like:
- three - [hri]
- throw - [hro]
- through, threw - [hrʉ]
- thrash - [hraʃ]
- thresh - [hrɛʃ]
- thrown, throne - [hron]
- thread - [hrɛd]
- threat - [hrɛt]
Children generally learn the less marked phonemes of their native language before the more marked ones. In the case of English-speaking children, /θ/ and /ð/ are often among the last phonemes to be learnt, frequently not being mastered before the age of five. Prior to this age, many children substitute the sounds [f] and [v] respectively. For small children, fought and thought are therefore homophones. As British and American children begin school at age four and five respectively, this means that many are learning to read and write before they have sorted out these sounds, and the infantile pronunciation is frequently reflected in their spelling errors: ve fing for the thing.
Children with a lisp, however, have trouble distinguishing /θ/ and /ð/ from /s/ and /z/ respectively in speech, using a single /θ/ or /ð/ pronunciation for both, and may never master the correct sounds without speech therapy. The lisp is a common speech impediment in English.
Foreign learners may have parallel problems. In English popular culture, the substitution of /z/ for /ð/ is a common way of parodying a French accent, but in fact learners from very many cultural backgrounds have difficulties with English dental fricatives, usually caused by interference with either sibilants or stops. Words with a dental fricative adjacent to an alveolar sibilant, such as clothes, truths, fifths, sixths, anesthetic, etc., are commonly very difficult for foreign learners to pronounce.
A popular advertisement for the Berlitz language school plays on the difficulties Germans may have with dental fricatives.
Phonology and distribution
In modern English, /θ/ and /ð/ bear a phonemic relationship to each other, as is demonstrated by the presence of a small number of minimal pairs: thigh:thy, ether:either, teeth:teethe. Thus they are distinct phonemes (units of sound, differences in which can affect meaning), as opposed to allophones (different pronunciations of a phoneme having no effect on meaning). They are distinguished from the neighbouring labiodental fricatives, sibilants and alveolar stops by such minimal pairs as thought:fought/sought/taught and then:Venn/Zen/den.
The vast majority of words in English with ⟨th⟩ have /θ/, and almost all newly created words do. However, the constant recurrence of the function words, particularly the, means that /ð/ is nevertheless more frequent in actual use.
The distribution pattern may be summed up in the following rule of thumb, which is valid in most cases: in an initial position, /θ/ is used except in certain function words; in a medial position, /ð/ is used except for certain foreign loan words; and in final position, /θ/ is used except in certain verbs. A more detailed explanation follows.
- Almost all words beginning with a dental fricative have /θ/.
- A small number of common function words (the Middle English anomalies mentioned below) begin with /ð/. The words in this group are:
- 1 definite article: the
- 4 demonstratives: this, that, these, those
- 2 personal pronouns each with multiple forms: thou, thee, thy, thine, thyself; they, them, their, theirs, themselves, themself
- 7 adverbs and conjunctions: there, then, than, thus, though, thence, thither (though in the United States thence and thither may be pronounced with initial /θ/)
- Various compound adverbs based on the above words: therefore, thereupon, thereby, thereafter, thenceforth, etc.
- A few words have an initial ⟨th⟩ for /t/ (e.g. Thomas): see below.
- Most native words with a medial ⟨th⟩ have /ð/.
- Between vowels (including r-colored vowels), followed by a weak vowel: heathen, farthing, fathom, Worthington; and the frequent combination -ther-: bother, brother, dither, either, farther, father, further, heather, lather, mother, northern, other, rather, smithereens, slither, southern, together, weather, whether, wither; Caruthers, Gaithersburg, Netherlands, Witherspoon, and similar compound names where the first component ends in '-ther' or '-thers'.
- Followed by /r/: brethren.
- A few native words have a medial /θ/:
- The adjective suffix -y normally leaves terminal /θ/ unchanged: earthy, healthy, pithy, stealthy, wealthy but worthy and swarthy have /ð/. Likewise verb inflexions and final -ly: earthing, frothed, fourthly, monthly, and the diminutive suffix -y in bothy (from booth).
- Some plurals have /θ/, as discussed in more detail below.
- Compound words in which the first element ends or the second element begins with ⟨th⟩ frequently have /θ/, as these elements would in isolation: bathroom, Southampton; anything, everything, nothing, something.
- The only other native words with medial /θ/ would seem to be brothel and Ethel.
- Most loan words with a medial ⟨th⟩ have /θ/.
- From Greek: Agatha, anthem, atheist, Athens, athlete, cathedral, Catherine, Cathy, enthusiasm, ether, ethics, ethnic, lethal, lithium, mathematics, method, methyl, mythical, panther, pathetic, sympathy
- From Latin: author, authority (though in Latin these had /t/; see below). Also names borrowed from or via Latin: Bertha, Gothic, Hathaway, Othello, Parthian
- From Celtic languages: Arthur (Welsh has /θ/ medially: /ærθɨr/); Abernathy, Abernethy
- From Hebrew: Ethan, Jonathan, Bethlehem, Bethany, leviathan, Bethel
- From German: Luther, as an anglicized spelling pronunciation (see below).
- Loanwords with medial /ð/:
- Greek words with the combination -thm-: algorithm, logarithm, rhythm. The word asthma may be pronounced /ˈæzðmə/ or /ˈæsθmə/, though here the ⟨th⟩ is nowadays usually silent.
- A few words have a medial ⟨th⟩ for /t/ or /th/ (e.g. lighthouse): see below.
- Nouns and adjectives
- Nouns and adjectives ending in a dental fricative usually have /θ/: bath, breath, cloth, froth, health, hearth, loath, mouth, sheath, sooth, tooth/teeth, width, wreath.
- Exceptions are usually marked in the spelling with -⟨the⟩: tithe, lathe, lithe with /ð/.
- blithe can have either /ð/ or /θ/. booth has /ð/ in England but /θ/ in America.
- Verbs ending in a dental fricative usually have /ð/, and are frequently spelled -⟨the⟩: bathe, breathe, clothe, loathe, scathe, scythe, seethe, sheathe, soothe, teethe, tithe, wreathe, writhe. Spelled without ⟨e⟩: mouth (verb) nevertheless has /ð/.
- froth has /θ/ whether as a noun or as a verb.
- The verb endings -s, -ing, -ed do not change the pronunciation of a ⟨th⟩ in the final position in the stem: bathe has /ð/, therefore so do bathed, bathing, bathes; frothing has /θ/. Likewise clothing used as a noun, scathing as an adjective etc.
- The archaic word ending "-eth" has /θ/.
- with has either /θ/ or /ð/ (see below), as do its compounds: within, without, outwith, withdraw, withhold, withstand, wherewithal, etc.
- Plural ⟨s⟩ after ⟨th⟩ may be realised as either /ðz/ or /θs/:
- Some plural nouns ending in ⟨ths⟩, with a preceding vowel, have /ðz/, although the singulars always have /θ/; however a variant in /θs/ will be found for many of these: baths, mouths, oaths, paths, sheaths, truths, wreaths, youths exist in both varieties; clothes always has /ðz/ (if not pronounced /kloʊz/, the traditional pronunciation).
- Others have only /θs/: azimuths, breaths, cloths, deaths, faiths, Goths, growths, mammoths, moths, myths, smiths, sloths, zeniths, etc. This includes all words in 'th' preceded by a consonant (earths, hearths, lengths, months, widths, etc.) and all numeric words, whether preceded by vowel or consonant (fourths, fifths, sixths, sevenths, eighths /eɪtθs/, twelfths, fifteenths, twentieths, hundredths /hʌndrədθs/, thousandths).
- Booth has /ð/ in the singular and hence /ðz/ in the plural for most speakers in England. In American English, it has /θ/ in the singular and /θs/ or /ðz/ in the plural. This pronunciation also prevails in Scotland.
In pairs of related words, an alternation between /θ/ and /ð/ is possible, which may be thought of as a kind of consonant mutation. Typically [θ] appears in the singular of a noun, [ð] in the plural and in the related verb: cloth /θ/, clothes /ð/, to clothe /ð/. This is directly comparable to the /s/-/z/ or /f/-/v/ alternation in house, houses or wolf, wolves. It goes back to the allophonic variation in Old English (see below), where it was possible for ⟨þ⟩ to be in final position and thus voiceless in the basic form of a word, but in medial position and voiced in a related form. The loss of inflections then brought the voiced medial consonant to the end of the word. Often a remnant of the old inflection can be seen in the spelling in the form of a silent ⟨e⟩, which may be thought of synchronically as a marker of the voicing.
Regional differences in distribution
The above discussion follows Daniel Jones' English Pronouncing Dictionary, an authority on standard British English, and Webster's New World College Dictionary, an authority on American English. Usage appears much the same between the two. Regional variation within standard English includes the following:
- The final consonant in with is pronounced /θ/ (its original pronunciation) in northern Britain, but /ð/ in the south, though some speakers of Southern British English use /θ/ before a voiceless consonant and /ð/ before a voiced one. A 1993 postal poll of American English speakers showed that 84% use /θ/, while 16% have /ð/ (Shitara 1993). (The variant with /ð/ is presumably a sandhi development.)
- In Scottish English, /θ/ is found in many words which have /ð/ further south. The phenomenon of nouns terminating in /θ/ taking plurals in /ðz/ does not occur in the north. Thus the following have /θs/: baths, mouths (noun), truths. Scottish English does have the termination /ðz/ in verb forms, however, such as bathes, mouths (verb), loathes, and also in the noun clothes, which is a special case, as it has to be clearly distinguished from cloths. Scottish English also has /θ/ in with, booth, thence etc., and the Scottish pronunciation of thither, almost uniquely, has both /θ/ and /ð/ in the same word. Where there is an American-British difference, the North of Britain generally agrees with the United States on this phoneme pair.
History of the English phonemes
Proto-Indo-European (PIE) had no dental fricatives, but these evolved in the earliest stages of the Germanic languages. In Proto-Germanic, /ð/ and /θ/ were separate phonemes, usually represented in Germanic studies by the symbols *đ and *þ.
- *đ (/ð/) was derived by Grimm's law from PIE *dʰ or by Verner's law (i.e. when immediately following an unstressed syllable) from PIE *t.
- *þ (/θ/) was derived by Grimm's law from PIE *t.
In West Germanic, the Proto-Germanic *đ shifted further to *d, leaving only one dental fricative phoneme. However, a new [ð] appeared as an allophone of /θ/ in medial positions by assimilation of the voicing of the surrounding vowels. [θ] remained in initial and presumably in final positions (though this is uncertain as later terminal devoicing would in any case have eliminated the evidence of final [ð]). This West Germanic phoneme, complete with its distribution of allophones, survived into Old English. In German and Dutch, it shifted to a /d/, the allophonic distinction simply being lost. In German, West Germanic *d shifted to /t/ in what may be thought of as a chain shift, but in Dutch, *þ, *đ and *d merged into a single /d/.
The whole complex of Germanic dentals, and the place of the fricatives within it, can be summed up in this table:
|PIE||Proto-Germanic||West Germanic||Old English||German||Dutch||Notes|
|*t||*þ||*[þ]||[θ]||/d/||/d/||Original *t in initial position, or in final position after a stressed vowel|
|*[đ]||[ð]||Original *t in medial position after a stressed vowel|
|*đ||*d||/d/||/t/||Original *t after an unstressed vowel|
|*dʰ||Original *dʰ in all positions|
|*d||*t||*t||/t/||/s/ or /ts/||/t/||Original *d in all positions|
Thus English inherited a phoneme /θ/ in positions where other West Germanic languages have /d/ and most other Indo-European languages have /t/: English three, German drei, Latin tres.
In Old English, the phoneme /θ/, like all fricative phonemes in the language, had two allophones, one voiced and one voiceless, which were distributed regularly according to phonetic environment.
- [ð] (like [v] and [z]) was used between two voiced sounds (either vowels or voiced consonants).
- [θ] (like [f] and [s]) was spoken in initial and final position, and also medially if adjacent to another unvoiced consonant.
Development up to Modern English
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The most important development on the way to modern English was the investing of the existing distinction between [ð] and [θ] with phonemic value. Minimal pairs, and hence the phonological independence of the two phones, developed as a result of three main processes.
- In early Middle English times, a group of very common function words beginning with /θ/ (the, they, there, etc.) came to be pronounced with /ð/ instead of /θ/. Possibly this was a sandhi development; as these words are frequently found in unstressed positions, they can sometimes appear to run on from the preceding word, which may have resulted in the dental fricative being treated as though it were word-internal.
- English has borrowed many words from Greek, including a vast number of scientific terms. Where the original Greek had the letter ⟨θ⟩ (theta), English retained the Late Greek pronunciation /θ/, regardless of phonetic environment (thermometer, methyl, etc.). In a few words of Indian origin, such as thug, ⟨th⟩ represents Sanskrit थ (/tʰ/) or ठ (/ʈʰ/), usually pronounced /θ/ (but occasionally /t/) in English.
- English has lost its original verb inflections. When the stem of a verb ends with a dental fricative, this was usually followed by a vowel in Old English, and was therefore voiced. It is still voiced in modern English, even though the verb inflection has disappeared leaving the /ð/ at the end of the word. Examples are to bathe, to mouth, to breathe.
Other changes that affected these phonemes included a shift /d/ → /ð/ when followed by unstressed suffix -er. Thus Old English fæder became modern English father; likewise mother, gather, hither, together, weather (from mōdor, gaderian, hider, tōgædere, weder). In a reverse process, Old English byrþen and morþor or myþra become burden and murder (compare the obsolete words burthen and murther).
Dialectally, the alternation between /d/ and /ð/ sometimes extends to other words, as bladder, ladder, solder with /ð/ (possibly being restricted elsewhere by the former two clashing with blather and lather). On the other hand, some dialects retain original d, and extend it to other words, as brother, further, rather. The Welsh name Llewelyn appears in older English texts as Thlewelyn (Rolls of Parliament (Rotuli parliamentorum) I. 463/1, King Edward I or II), and Fluellen (Shakespeare, Henry V). Th also occurs dialectally for wh, as in thirl, thortleberry, thorl, for whirl, whortleberry, whorl. Conversely, Scots has whaing, whang, white, whittle, for thwaing, thwang, thwite, thwittle.
The old verb inflection -eth (Old English -eþ) was replaced by -s (he singeth → he sings), not a sound shift but a completely new inflection, the origin of which is still being debated. Possibilities include alveolarization (since s is easier to pronounce there than th), or displacement by a nonstandard English dialect.
History of the digraph
⟨th⟩ for /θ/ and /ð/
Though English speakers take it for granted, the digraph ⟨th⟩ is in fact not an obvious combination for a dental fricative. The origins of this have to do with developments in Greek.
Proto-Indo-European had an aspirated /dʱ/ that came into Greek as /tʰ/, spelled with the letter theta. In the Greek of Homer and Plato, this was still pronounced /tʰ/, and therefore when Greek words were borrowed into Latin, theta was transcribed with ⟨th⟩. Since /tʰ/ sounds like /t/ with a following puff of air, ⟨th⟩ was the logical spelling in the Latin alphabet.
By the time of New Testament Greek (koiné), however, the aspirated stop had shifted to a fricative: /tʰ/→/θ/. Thus theta came to have the sound that it still has in Modern Greek, and which it represents in the IPA. From a Latin perspective, the established digraph ⟨th⟩ now represented the voiceless fricative /θ/, and was used thus for English by French-speaking scribes after the Norman Conquest, since they were unfamiliar with the Germanic graphemes ð (eth) and þ (thorn). Likewise, the spelling ⟨th⟩ was used for /θ/ in Old High German prior to the completion of the High German consonant shift, again by analogy with the way Latin represented the Greek sound. It also appeared in early modern Swedish before a final shift to /d/.
The history of the digraphs ⟨ph⟩ for /f/ and ⟨ch⟩ for Scots, Welsh or German /x/ is parallel.
⟨th⟩ for /t/
Since neither /tʰ/ nor /θ/ was a native sound in Latin, the tendency must have emerged early[speculation?], and at the latest by medieval Latin, to substitute /t/. Thus, in many modern languages, including French and German, the ⟨th⟩ digraph is used in Greek loan-words to represent an original /θ/, but is now pronounced /t/: examples are French théâtre, German Theater. In some cases, this etymological ⟨th⟩, which has no remaining significance for pronunciation, has been transferred to words in which there is no etymological justification for it. For example, German Tal ('valley', cognate with English dale) appears in many place-names with an archaic spelling Thal (contrast Neandertal and Neanderthal). The German family names Theuerkauf and Thürnagel are other examples. The German spelling reform of 1901 largely reversed these, but they remain in some proper nouns.
Examples of this are also to be found in English, perhaps influenced immediately by French. In some Middle English manuscripts, ⟨th⟩ appears for ⟨t⟩ or ⟨d⟩: tho 'to' or 'do', thyll till, whythe white, thede deed. In Modern English we see it in Esther, Thomas, Thames, thyme, Witham (the town in Essex, not the river in Lincolnshire which is pronounced with /ð/) and the old spelling of Satan as Sathan.
In a small number of cases, this spelling later influenced the pronunciation: amaranth, amianthus and author have spelling pronunciations with /θ/, and some English speakers use /θ/ in Neanderthal.
⟨th⟩ for /th/
A few English compound words, such as lightheaded or hothouse, have the letter combination ⟨th⟩ split between the parts, though this is not a digraph. Here, the ⟨t⟩ and ⟨h⟩ are pronounced separately (light-headed) as a cluster of two consonants. Other examples are anthill, goatherd, lighthouse, outhouse, pothead; also in words formed with the suffix -hood: knighthood, and the similarly formed Afrikaans loanword apartheid. In a few place names ending in t+ham, the t-h boundary has been lost and become a spelling pronunciation, for example Grantham.
- English pronunciation
- Received Pronunciation
- Spelling pronunciation
- Non-native pronunciations of English
- English orthography
- Roach, Peter (2009). English Phonetics and Phonology. Cambridge University Press. p. 112. ISBN 978-0-521-71740-3.
- Gramley, Stephan; Pátzold, Michael (2004). A Survey of Modern English. Routledge. p. 76. ISBN 978-1-134-42046-9.
- Collins, Beverley; Mees, Inger M. (2013). Practical Phonetics and Phonology: A Resource Book for Students. Routledge. p. 122. ISBN 978-0-415-50649-6.
- Shockey, Linda (2003). "2.5.1 ð-reduction". Sound Patterns of Spoken English. pp. 43–44.
- Bauer, Laurie; Lieber, Rochelle; Plag, Ingo (2015). The Oxford Reference Guide to English Morphology. Oxford University Press. p. 131. ISBN 978-0-19-874706-2.
- Collins, Beverley; Mees, Inger M. (2013). Practical Phonetics and Phonology: A Resource Book for Students. Routledge. p. 127. ISBN 978-0-415-50649-6.
- Jones, Daniel (2006). "Introduction". In Roach, Peter; Hartman, James; Setter, Jane. Cambridge English Pronouncing Dictionary (17th ed.). Cambridge University Press. ISBN 0-52168086-7.
- In fact, some linguists see 'em as originally a separate word, a remnant of Old English hem, but as the apostrophe shows, it is perceived in modern English as a contraction of them. See Online Etymology Dictionary. 'em. Retrieved on 18 September 2006.
- Wright (1981:137)
- Wells (1982:329)
- Phonological Features of African American Vernacular English
- The American Heritage Dictionary, 1969.
- Kenyon, John S.; Knott, Thomas A. (1953) . A Pronouncing Dictionary of American English. Springfield, Mass.: Merriam-Webster. p. 87. ISBN 0-87779-047-7.
- Collins, Beverley; Mees, Inger M. (2013) [First published 2003], Practical Phonetics and Phonology: A Resource Book for Students (3rd ed.), Routledge, ISBN 978-0-415-50650-2
- Shitara, Yuko (1993). "A survey of American pronunciation preferences." Speech Hearing and Language 7: 201–32.
- Wells, John C. (1982), Accents of English 2: The British Isles, Cambridge: Cambridge University Press, ISBN 0-521-24224-X
- Wright, Peter (1981), Cockney Dialect and Slang, London: B.T. Batsford Ltd.