Hittite phonology is the description of the reconstructed phonology or pronunciation of the Hittite language. Because Hittite as a spoken language is extinct, thus leaving no living daughter languages, and no contemporary descriptions of the pronunciation are known, little can be said with certainty about the phonetics and the phonology of the language. Some conclusions can be made, however, by noting its relationship to the other Indo-European languages, by studying its orthography and by comparing loanwords from nearby languages.
Hittite had two series of consonants, which may be described as fortis and lenis; one was written always geminate in the original script, and the other was always written simple. In cuneiform, all consonants sounds except for glides could be geminate. It has long been noticed that the geminate series of plosives is the one descending from Proto-Indo-European voiceless stops, and the simple plosives come from both voiced and voiced aspirate stops. This is often referred as Sturtevant's law. Because of typological implications of Sturtevant's law, the distinction between the two series is commonly regarded as one of voice. However, there is still disagreement over the subject among scholars, some of whom view both series as if they were differentiated by length, which a literal interpretation of the cuneiform orthography would suggest.
Supporters of a length distinction usually point to the fact that Akkadian, the language from which the Hittites borrowed the cuneiform script, had voicing. Hittite scribes nevertheless used voiced and voiceless signs interchangeably. Kloekhorst has also argued that the absence of assimilatory voicing is also evidence for a length distinction and points out that the word "e-ku-ud-du - [g?tu]" does not show any voice assimilation. However, if the distinction were one of voice, agreement between the stops should be expected since the velar and the alveolar plosives are known to be adjacent since the "u" in that word does not stand for a vowel but instead represents labialization.
All resonants in Hittite coincide with their respective etymological pronunciations in Proto-Indo-European, which makes it unlikely that they were pronounced differently. Just like in the parent language, in Hittite resonants were syllabic interconsonantally. They were written in Hittite with cuneiform sign containing the vowel "a" (wa-a-tar - [wá:dr?], la-a-ma-an - [lá:mn?]). However, it is not well known if Hittite inherited the bilabial syllabic nasal. In final position, Hittite added an epenthetic vowel /?/ (Hittite e-?u-un - [:s?n] < Proto-Indo-European *h?és-m?). Some cognates may point that Proto-Indo-European *m? merged with Hittite /a/ in medial and initial position.
The affricate is written in Hittite with signs containing a "z" and is known to have as a main phonological source the affrication of a "*t". In the prehistory of Hittite, a "*t" could be affricated if it was followed by "*s" or by "*i?". That is known since "t"-stem nouns have a nominative ending in "z" and some verbal desinences descended from a prehistorical sequence "*ti". Therefore, the following development is usually assumed [t:j] > [t:?] > [t] > [t] > [t?s]. However, nothing excludes the possibility of it being pronounced as a post-alveolar or palatal affricate. A secondary source of the sign "z" is an early Indo-European dissimilation that occurred between two adjacent dentals, which consisted in the insertion of "*s" between them (e-ez-du - [:t?stu] < "*h?éd-tu").
Some advocates of a voice/voiceless series propose a voiced counterpart, which is rather controversial, and claim that whenever "z" was geminate, it represented [t?s] and that when it was simple, it was pronounced [d?z].
Hittite is believed to have had a sibilant, a uvular fricative and a labialized uvular fricative. They were written in the original script with signs containing "?" and "?". In Akkadian cuneiform, they originally stood for a voiceless alveolar fricative and a voiceless velar fricative, respectively.
It can be said with confidence that "?" stood for a single phoneme. Although the exact place of articulation of the Hittite phoneme written with signs having an "?" cannot be determined with absolute certainty, there are various arguments for assuming it to have been an alveolar sibilant. Typologically, if a language has fricatives, it almost certainly has /s/, and languages that lack both phonemes are rare. Morover, /s/ is known to descent from Proto-Indo-European *s, which is uncontroversially reconstructed as a voiceless alveolar sibilant.
Furthermore, the signs that the Hittite scribes adopted for "?" stood in Akkadian for [s] as well. It has been noted also that "?" appears in Ugaritic loanwords as ?, such as the Hittite royal name "?uppiluliuma", which is written in Ugaritic as ?pllm". Given that Semitic *? merged with *? in Ugaritic, also suggesting a pronunciation of [s]. It has also been noted that Hittite royal names containing an "?" are written in Egyptian Hieroglyphs with the sign that is conventionally transcribed as "?". Finally, it is believed among scholars that Indo-European diphthongs *oi and *ou changed to Hittite "?" and "?", respectively, unless an alveolar consonant followed them, one of which is /?/, which reinforces the idea that it was alveolar in Hittite.
It can be held with certainty that /?/ was a form of fricative, but its place of articulation is not so well understood. There is some evidence that may point towards a uvular/velar place of articulation. In Akkadian, the signs for "?" had a velar place of articulation, and the sound was always voiceless. Furthermore, Ugaritic borrowings from Hittite commonly transcribe "?" as "?", which stands for a voiced velar fricative (e.g d < duui?, td?l < mTud?aliya, tr?nds< URUTar?untaa). However, it has also occasionally been transcribed as a voiceless pharyngeal fricative ("?t? < ?attu?"). Some scholars have interpreted it as a velar fricative. Nonetheless, neither language could distinguish velar from uvular fricatives. Other scholars have suggested that the Ugaritic evidence may show that "?" represented more than one phoneme.
Known to descend from Proto-Indo-European "*h?", "?" is believed to descend from "*h?" as well according to the laryngeal theory. In Proto-Indo-European, "*h?" is known for coloring *e to *a. It has also been shown that "?" colors neighboring /u/ to /?/. Its coloring qualities in Hittite and Proto-Indo-European suggest a uvular place of articulation since uvular consonants are usually incompatible with advanced tongue root since they cause retraction of adjacent vowels. Moreover, a velar place of articulation could be dismissed since they do not typically color vowels but are instead more commonly influenced by vowels. Similarly, that evidence precludes the possibility of "?" being a pharyngeal fricative, which usually triggers the fronting, rather than retraction, of vowels (e.g Proto-Semitic *?arum > Akkadian erum).
The natural outcome of "*h?" is a geminate "", indicating a voiceless manner of articulation. Nevertheless, the scholars who support the fortis/lenis framework usually interpret it as a fortis consonant. Notably, it is also subject to Eichner's voicing rules. In other words, if a voiceless "?" occurred intervocalic position between two unaccented syllables or after a long accented syllable, it would be regularly voiced. Therefore, a phonemic distinction between "" and "?" can be observed in the Hittite lexicon, just like in the stop system. Eichner's voicing law has also been observed in other Anatolian languages like Lycian (compare the verbal decinence Hittite -a?ari and Lycian -?agã).
Hittite had four labialized obstruents: two velar plosives and two uvular fricatives.
Labialized velars are known to have developed from the Proto-Indo-European labiovelars. A classic example is the Proto-Indo-European root verb "*h?égti ~ *h?génti" > "ekuzi ~ akuanzi". The idea that Hittite preserved Indo-European labiovelars as labialized velars instead of a velar + w, like in other centum languages, is supported by various anomalies in verbal roots containing labialized obstruents. For example, the first-person singular aorist of ekuzi "to drink" is "e-ku-un - [gn]". However, if the "u" is vocalic, the expected *e-ku-nu-un occurs, as in Hittite vocalic stemmed verbs. That view is also strengthened by the first-person plural present form "a-ku-e-ni - [agwni]", instead of the expected *a-ku-me-ni, as in Hittite true verbal u-stems.
It has also been noted that it can be written as "e-uk-zi - [g?t?si]", which has been pointed out as an argument for assuming labialization as well, in which case the rounding happened with at the same time as the plosive instead of following it as a semivowel. The phenomena have also been attested in other verbs such as tarukzi/tarkuzi "he/she dances".
Similar observations can be made about the verb taruu- [tr-] "to overpower". Like the verb "eku-", "taruu-" also has an irregular first-person aorist for an u-stem noun (ta-ru-u?-?u-un instead of *ta-ru-u?-?u-un-un) and an irregular first person-plural aorist (tar-?u-u-en instead of *tar-u?-me-en). That would suggest that the Proto-Indo-European sequence "h?u?" became Hittite ?u-u . Evidence of laryngeal labialization has been found outside Hittite: Lycian has Trqqñt- "Stormgod" < tr?h?u?ént- "powerful", the "q" most likely representing a labialized velar plosive descending from the Proto-Indo-European segmental sequence "h?u?". Therefore, some scholars have regarded it to be an Anatolian feature, not exclusive to Hittite.
It was debated by scholars whether Hittite had a vowel phoneme /?(:)/, distinct from the vowel /u(:)/. The idea that the sign "u" stood for /?(:)/ and "ú" for /u(:)/ was first proposed by Weidner since such a practice was paralleled in Hurrian and Akkadian. It had mainstream support only when Kloekhorst published in 2008 a detailed analysis of the distribution of both signs and showed that they appeared partially in a partial complementary distribution.
Plene spelling is the practice of writing a vowel redundantly. Its use was never consistent at any stage of Hittite, but it was generally more common in earlier texts. It certainly must have represented some phonemic features, most obviously vowel length, as in ne-e-pí-i?, which should be analyzed phonologically as [n:bis]. It has been argued that it could represent stress as well.