They are also distinguished by other phonetic markers: the fortis /θ/ is pronounced with more muscular tension than the lenis /ð/; and /θ/ is more strongly aspirated than /ð/, as can be demonstrated by holding a hand in front of the mouth as they are spoken.
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.
Regional variation within standard English includes the following: Proto-Indo-European (PIE) had no dental fricatives, but these evolved in the earliest stages of the Germanic languages.
The most important development on the way to modern English was the investing of the existing distinction between [ð] and [θ] with phonemic value.
In a reverse process, Old English byrþen and morþor or myrþra become burden and murder (compare the obsolete variants 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).
The Welsh name Llewelyn appears in older English texts as Thlewelyn (Rolls of Parliament (Rotuli parliamentorum) I.
Conversely, Scots has whaing, whang, white, whittle, for thwaing, thwang, thwite, thwittle.
To speakers of varieties in which /θ/ and /ð/ are pronounced [θ] and [ð], fronting and stopping are generally considered to have less of a marked contrast with the standard pronunciation than alveolarization, which is often more stigmatized.
In some areas, such as London, and certain dialects, including African American Vernacular English and less commonly New Zealand, many people realize the phonemes /θ/ and /ð/ as [f] and [v], respectively.
Although traditionally stigmatized as typical of a Cockney accent, this pronunciation is fairly widespread, especially when immediately surrounded by other fricatives for ease of pronunciation, and has, in the early 20th century, become an increasingly noticeable feature of the Estuary English accent of South East England.
In rarer or older varieties of African American Vernacular English, /θ/ may be pronounced [s] after a vowel and before another consonant, as in bathroom [ˈbæsɹum].
Due to the said ridicule, learners who are unable to realize these sounds sometimes opt for the less marked th-fronting or th-stopping instead of alveolarization.
[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.
[citation needed] The existing and particular lexical distribution of th-debuccalization imposes special constraints on the progress of th-fronting in Glasgow.
The replacement of /θr/ with [hr] leads to pronunciations like: As with many English consonants, a process of assimilation can result in the substitution of other speech sounds in certain phonetic environments.
[8][9][10][11] The resulting consonant is usually long (geminated) which may be the only audible cue for the speaker to distinguish particular words (for example, the definite and indefinite articles, compare "run the mile" [ˈɹʌn̪ n̪ə ˈmaɪl] and "run a mile" [ˈɹʌn ə ˈmaɪl]).
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.
Learners from very many cultural backgrounds have difficulties with English dental fricatives, usually caused by interference with either sibilants or stops.
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).
For example, German Tal ('valley', cognate with English dale) appears in many place-names with an archaic spelling Thal (contrast Neandertal and Neanderthal).
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.
More recently, the name of the capital of Nepal was often written Katmandu down to the late 20th century, but is now usually spelt Kathmandu.
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.
In a few place names ending in t+ham, the t-h boundary has been lost and become a spelling pronunciation, for example Grantham.