Voiceless dental fricative
The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in think. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential (see below). The symbol in the International Phonetic Alphabet that represents this sound is ⟨θ⟩, and the equivalent X-SAMPA symbol is
T. The IPA symbol is the Greek letter theta, which is used for this sound in post-classical Greek, and the sound is thus often referred to as "theta".
|Voiceless dental fricative|
The dental non-sibilant fricatives are often called "interdental" because they are often produced with the tongue between the upper and lower teeth, and not just against the back of the upper or lower teeth, as they are with other dental consonants.
This sound and its voiced counterpart are rare phonemes occurring in 4% of languages in a phonological analysis of 2,155 languages. Among the more than 60 languages with over 10 million speakers, only English, various dialects of Arabic, Standard Peninsular Spanish, Swahili (in words derived from Arabic), and Greek have the voiceless dental non-sibilant fricative. Speakers of languages and dialects without the sound sometimes have difficulty producing or distinguishing it from similar sounds, especially if they have had no chance to acquire it in childhood, and typically replace it with a voiceless alveolar fricative (/s/) (as in Indonesian), voiceless dental stop (/t/), or a voiceless labiodental fricative (/f/); known respectively as th-alveolarization, th-stopping, and th-fronting.
The sound is known to have disappeared from a number of languages, e.g. from most of the Germanic languages or dialects, where it is retained only in Scots, English, Elfdalian, and Icelandic, but it is alveolar in the last of these. Among non-Germanic Indo-European languages as a whole, the sound was also once much more widespread, but is today preserved in a few languages including the Brythonic languages, Peninsular Spanish, Galician, Venetian, Albanian, some Occitan dialects and Greek. It has likewise disappeared from many Semitic languages, such as Hebrew (excluding Yemenite Hebrew) and many modern varieties of Arabic (excluding Tunisian, Mesopotamian Arabic and various dialects in the Arabian Peninsula).