|Native to||United States|
|Region||Caddo County in western Oklahoma|
|Native speakers||25 (1997)|
Caddo is the only surviving Southern Caddoan language of the Caddo language family. It is spoken by the Caddo Nation of Oklahoma. Today, only 25 elderly speakers are estimated to remain, none of whom are monolingual Caddo speakers, making Caddo a critically endangered language. There are several mutually intelligible dialects of Caddo; some of the more prominent dialects include Kadohadacho, Hasinai, Hainai, Natchitoches, and Yatasi. Today, the most commonly used dialects are Hasinai and Hainai. Caddo is linguistically related to the members of the Northern Caddoan language family; these include the Pawnee-Kitsai (Keechi) languages (Arikara, Kitsai, and Pawnee) and the Wichita language. Kitsai is now extinct, and Pawnee, Arikara, and Wichita each have fewer surviving speakers than Caddo does. Another language, Adai, is postulated to have been a Caddoan language while it was extant, but because of scarce resources and the language’s extinct status, this connection is not conclusive, and Adai is generally considered a language isolate.
Use and language revitalization efforts 
As of 2012, the Caddo Nation teaches weekly language classes; language CDs, a coloring book, and an online learning website are also available. As of 2010, a Caddo app is available for Android phones.
Caddo has nineteen contrastive consonants, which is a normal-sized consonant inventory. It is somewhat unusual in that it lacks lateral consonants. The IPA symbols for the consonants of Caddo are given below:
Caddo has three contrastive vowel qualities, /i/, /ɑ/, and /u/, and two contrastive vowel lengths, long and short, for a total of 6 vowel phonemes.
|High||i iː||u uː|
However, there is a great deal of phonetic variation amongst the short vowels. The high front vowel /i/ is generally (but not always) realized as its lower counterpart /ɪ/, and the high back vowel /u/ is similarly often realized as its lower counterpart /ʊ/. The low central vowel /a/ has a wider range of variation, pronounced (most commonly) as /ɐ/ when followed by any consonant except a semivowel or a laryngeal consonant, as a low central vowel (for which IPA lacks a symbol) at the end of an open syllable or when followed by a laryngeal consonant, and as /ə/ before a semivowel.
In general, the long vowels do not feature this kind of variation, but are simply lengthened versions of the phonemes represented in the chart.
Caddo also has four diphthongs, which can be written a number of different ways; the transcription below shows the typical Caddo Nation orthography (a vowel paired with a glide) and the IPA version, represented with vowels and offglides.
- ay /aj/ – Pronounced like English ‘eye’
- aw /aw/ – Pronounced like ‘’ou’’ in English ‘out’
- iw /iw/ – Pronounced like English ‘ew’
- uy /uj/ – Pronounced like ‘’uoy’’ in English ‘buoy’
Caddo is a tone language. There are three tones in Caddo: low tone, which is unmarked (a); high tone, which is marked by an acute accent over the vowel (á); and falling tone, which is always long, and marked by a grave accent over the vowel (àː).
Tone occurs both lexically (as a property of the word), non-lexically (as a result of tonological processes), and also as a marker of certain morphological features; for instance, the past tense marker is associated with high tone.
Tonological processes 
There are three processes that can create non-lexical high tone within a syllable nucleus. (Note: see the section below for an explanation of other phonological changes which may occur in the following examples.)
- 1. H-deletion
- VhCC → VHighCC
- An /h/ before two consonants is deleted and the preceding vowel gains high tone.
- Ex: /kiʃwɑhn-t-ʔuh/ → [kiʃwɑ́nːt’uh] ‘parched corn’
- 2. Low tone-deletion
- VRVLowC → VHighRC
- A low tone vowel following a resonant (sonorant consonant) is deleted and the preceding vowel gains high tone.
- Ex: /sa-baka-nah-hah/ → [sawkɑ́nːhah] ‘does he mean it?’
- 3. Backwards assimilation
- VRVHigh → VHighRVHigh
- A vowel preceding a resonant and a high tone vowel gains high tone.
- Ex: /nanɑ́/ → [nɑ́nɑ́ː] ‘that, that one’
Phonological processes 
Vowel syncope 
There are two vowel syncope processes in Caddo, which both involve the loss of a low-tone vowel in certain environments. The first syncope process is already described as Low tone-deletion (above). The second syncope process is described below:
- Interconsonantal Syncope
- VCVLowCV → VCCV
- A low-tone vowel in between a vowel-consonant sequence and a consonant-vowel sequence is deleted.
- Example (shown with intermediary form): /kak#(ʔi)t’us-jaʔah/ → kahʔit’uʃaʔah → [kahʔit’uʃʔah] ‘foam, suds’
Consonant cluster simplification 
As a result of the syncope processes described above, several consonant clusters emerge which are then invariably simplified by way of phonological process. At the present stage of research, these processes seem to be unrelated, except that they represent a phonetic reduction in consonant clusters; therefore, they are listed below without much further explanation.
- 1. nw → mm
- 2. tw → pp
- 3. tk → kk
- 4. n → m / __ [+labial]
- 5. ʔʔ → ʔ
- 6. hh → h
- 7. ʔ+Resonant → Resonant+ʔ / syllable final
Syllable coda simplification 
Similar to the consonant cluster simplification process, there are four processes by which a syllable-final consonant is altered.
- 1. b → w / syllable final
- 2. d → t / syllable final
- 3. k → h / syllable final (but not before k)
- 4. tʃ → ʃ / syllable final
Word boundary processes 
There are three word-boundary processes in Caddo, all of which occur word-initially:
- 1. n → t / # __
- 2. w → p / # __
- 3. y → d / # __
- Ex. /ni-huhn-id-ah/ → [tihúndah] ‘she returned it’
These processes are generally not applicable in the case of proclitics (morphemes which behave like an affix and are phonologically dependent on the morpheme they are attached to, e.g. an apple in English).
Caddo has a glottalization process by which any voiceless stop or affricate (except p) becomes an ejective when followed by a glottal stop.
- [-sonorant, -continuant, -voice, -labial, -spread glottis] → [+constricted glottis] / ___ [+constricted glottis, -spread glottis]
- A voiceless stop or affricate (except p) becomes an ejective when followed by a glottal stop.
- Ex. /sik-ʔuh/ → [sik’uh] ‘rock’
Caddo has a palatalization process which affects certain consonants when followed by /j/, with simultaneous loss of the /j/.
- a) /kj/ → [tʃ]
- b) /sj/ → [ʃ]
- Ex. /kak#ʔa-k’as-jaʔah/ → [kahʔak’a ʃʔah] ‘one’s leg’
(Melnar includes a third palatization process, /tj/ → [ts]. However, /ts/ is not a palatal affricate, so this process has not been included here. Nevertheless, it is probably the case that this third process does occur.)
Caddo has three processes by which a syllable nucleus (vowel) may be lengthened.
- Syllable Lengthening Process One
- VHigh(Resonant)CVC# → VHigh(Resonant)ːCVC#
- When the second-to-last syllable in a word has a nucleus consisting of a high tone vowel (and, optionally, a resonant), and the last syllable has the form CVC, then the high tone nucleus is lengthened.
- Ex. /bak-‘ʔawɑ́waʔ/ → [bahʔwɑ́ːwaʔ] ‘they said’
- Syllable Lengthening Process Two
- V(Resonant)ʔ → V(Resonant) ː / in any prepenultimate syllable
- In any syllable before the penultimate, a glottal stop coda is deleted, and the remaining nucleus is lengthened.
- Ex. /hɑ́k#ci-(ʔi)bíhn-saʔ/ → [hɑ́hciːbíːsaʔ] ‘I have it on my back’
- Syllable Lengthening Process Three
- a) ij → iː
- b) uw →uː
- Any syllable nucleus consisting of ij or uw must convert to a long vowel.
Education and preservation attempts 
The Caddo Nation is making a concentrated effort to save the Caddo language. The Kiwat Hasinay ('Caddo Home') foundation, located at the tribal home of Binger, Oklahoma, offers regular Caddo language classes, in addition to creating dictionaries, phrase books, and other Caddo language resources. They have also made a long-term project of trying to record and digitally archive Caddoan oral traditions, which are an important part of Caddo culture.
- "Caddo." Ethnologue. Retrieved 16 Feb 2013.
- The Linguist List
- SIL International, 2009
- Caddo Nation, 2007
- Native Languages of the Americas, 2011
- "Caddo Nation - Language". The Caddo nation. Retrieved 2012-10-30.
- "The Caddo Language Learning Tool". Retrieved 2012-10-30.
- "Caddo Language App Now Available on Android Market". alterNative Media. Retrieved 2012-10-30.
- World Atlas of Language Structures Online
- Melnar, 2004
- Kiwat Hasinay Foundation, 2005
- Caddo Nation. 2007. Caddo Nation – Language. (October 20, 2011).
- Kiwat Hasinay Foundation. 2005. Kiwat Hasinay Foundation. (October 20, 2011).
- Melnar, Lynette R. 2004. Caddo Verb Morphology. Lincoln: University of Nebraska Press.
- Native Languages of the Americas. 2011. Caddo Language and the Caddo Indian Tribe (Kadohidacho, Hasinai, Hasinay). (October 20, 2011).
- SIL International. 2009. Caddo. Ethnologue: Languages of the World, 16th Edition. (October 20, 2011).
- The Linguist List. Caddo – MultiTree. (October 20, 2011).
- World Atlas of Language Structures Online. Caddo. (October 20, 2011).
- Ethnologue report for Caddo
- Kiwat Hasinay Foundation
- Caddo Alphabet (PDF)
- Kúhaʔahat Oklahoma! - How to say "hello" in Caddo
- Caddo Indian Language (Hatsinai)
- Search-able Caddo Language Dictionary on Socrata, created by Michael Sheyahshe (replaces Caddo WebLEX)
- OLAC resources in and about the Caddo language