Vowels

Koasati has three vowels, all of which occur as short and long and can be nasalized. The following chart is based on Kimball's work. Kimball describes what is normally the close-mid back vowel /o/ as "high back" vowel, hence its placement in the chart below.^[5] He notes that /o/ sometimes has the allophone [u] and is raised to [ʊ] in closed word-final syllables.

In 2007, the Coushatta Tribe of Louisiana developed and approved its own orthographic system.^[6] In this system, long vowels are written by doubling the vowel (e.g., [aː] as aa), and nasalized vowels are underlined (e.g., [õ] or [ǫ] as o̱).

Vowel length in Koasati can be contrastive. For example, vowel length distinguishes meaning for palana "bean" and palaana "plate", as well as choba "big" and chooba "horse". Vowel nasalization most often occurs word-finally as a phrase-terminal marker. In Koasati, the end of a phrase is basically marked by either deletion of the final unaccented vowel or the nasalization of the final vowel when deleting it would eliminate phonological information relevant to the phrase's meaning. For example, the final vowel in hopoonilaho̱ "he/she will cook it" is nasalized instead of deleted, and therefore is distinguished from the more emphatic hopoonilaha̱, where the irrealis future suffix -laha- indicates that the action will certainly occur, whereas the irrealis future suffix -laho- does not provide such certainty.

Consonants

Koasati has the consonants given in the table below, based on Geoffrey Kimball's work.^[7] IPA transcriptions occur in brackets when different from the orthography provided by Kimball.

Not included in this chart is a glottal glide (marked ꞉) that Kimball uses in his own consonant chart, presumably to represent the lengthened vowel sounds of Koasati. In the Tribe's official orthography, the [ɬ] is represented by ⟨th⟩ and the [t͡ʃ] is represented by ⟨ch⟩, with no distinction for aspiration. Additionally, Kimball notes that /p/, /t/, and /k/ are aspirated in initial and medial positions. However, the website for the Koasati Language Project explicitly states that these consonants are never aspirated.^[8] The [ɦ] occurs most often before [t͡ʃ], as in [haɦt͡ʃí] "river", spelled ⟨hahchi⟩ in the official orthography, thereby distinguished from ⟨hachi⟩ "tail".

Syllable structure

Koasati has both light (CV, VC, V) and heavy (CVC) syllables. Consonant clusters occur across syllables but not within. All monomorphemic Koasati words end in light syllables, while the penultimate syllable can be light but is usually heavy, and it is usually preceded by one or more light syllables, as with the construction CV.CVC.CV as in the word holihtá "fence". Other shapes, in which one or more heavy syllables precede a heavy penultimate syllable (e.g. CV.CVC.CVC.CV as in hacokpalpá "butterfly"), or alternate heavy and light syllables (e.g. CVC.CV.CVC.CV. as in pa꞉piyá꞉ka "bridge"), are usually the result of the compounding of two words or a once-productive rule of syncope in which the vowel of every second syllable except the final syllable was deleted. Vowel clusters occur in Koasati, unlike in other Muskogean languages where such clusters are made impossible by metathesis and vowel deletion. These clusters occur in Koasati due to the use of locative prefixes that end in a vowel and class 1A negative transitive verbs since these do not undergo the processes of metathesis and vowel deletion. Clusters beginning with /a꞉/ and /i꞉/ are most frequent, and all clusters are generally spoken with a glottal stop between vowels.

Tone

Koasati has low [ ` ], high [ ´ ], and high rising–falling [ ˇ ] pitch accents, as well as a fourth unmarked mid-level tone. All noun roots must have one high-pitch accented syllable. The location of the accent depends on the properties of the penultimate syllable. With a few exceptions, the accent falls on the final syllable unless the penultimate syllable contains a long vowel. These pitch accents can be contrastive, as with sakihpǫ́ 'It is a mink.' and sakíhpǫ 'It is not air-dried.'. Pitch placement on verbs is motivated by morphology. Most indicative verbs take the high accent, though a few take the low accent. Intensive verbs take the high rising–falling accent.

Phonological processes

• /c/ in Kimball's orthography, or /ch/ in the official Tribe orthography, is sometimes realized as [ts] before resonants: cf. awó yáhci "it is just like grandpa" is realized as [awó yahtsi].
• In rare cases, /k/ is labialized to [kʷ] before /o/: cf. akkó "that" → [akkʷó]
• /s/ has the palatal allophone [š] word-initially before /o/ and intervocalically: cf. sopátlit "she cleaned it" → [šopátlit]
• When /s/ occurs both before and after a vowel, the allophone of the first /s/ harmonizes with that of the second. For example, sóslit ('he skinned them') is not pronounced [šoslit] but [sóslit].
• Rarely, /s/ can have the allophone [r] when it occurs word-finally: cf. o꞉támmo꞉s "it is just sunset" → [o꞉támmo꞉r]
• In the word-final position, /h/ becomes a voiceless continuation of the vowel it follows. This can also occur following vowels in other positions. For example, iltóhnot "she worked" becomes [iltóónot].
• /h/ can be voiced to [ɦ], usually before c, as discussed above with [haɦchi].
• /l/ is sometimes realized as /n/, as with intolihná "work" → [iltolihná]. Rarely, it is realized as [r] intervocalically.
• The vowel /i/ shifts to [ɪ] in all closed syllables, and /o/ shifts to [ʊ] when it occurs in closed word-final syllables: cf. hókfit "she put it on" → [hókfɪt]; íkbot "he did not kill it" → [íkbʊt]
• The vowels /i/ and /o/ also rarely have the allophones [ɛ] and [u] respectively, though the underlying reason is unclear: cf. yilahá "orange (fruit)" → [yɛlahá]; solitá꞉wa "soldier" → [sulitá꞉wa]

Nouns

Two sets of prefixes mark noun possession in Koasati. The am-set generally identifies alienable possession and a relatively small set of kinship terms and body parts, while the ca-set identifies inalienable possession and most kinship terms and body parts. These prefixes mark person and number on possessing nouns as follows:

Verbs

Word order

Koasati sentences generally follow a subject, object, verb (SOV) pattern. If an indirect object is present, the order is typically subject, indirect object, verb (SIoV). For sentences with both a direct and indirect object, the order is typically subject, object, verb, indirect object (SOVIo), though SIoOV also occurs. Any locatives tend to follow the verb. Because Koasati uses the nominative case, these orders are not rigid - elements can be moved within the sentence for emphasis. Examples of some basic orders follow:

• SOV

• SOVIo

Case marking

Koasati is an active–stative language. It has seven cases that can be used across five classes of nouns:

The five noun classes contain the following types of nouns, followed by examples:

• Class I: nouns for animate objects (ifá, "dog")
• Class II: nouns to or in which action can occur (ó꞉la, "town")
• Class III: nouns within or among which action can occur (í꞉sa, "house")
• Class IV: nouns describing an area where action can occur (caffá, "field")
• Class V: personal names, kinship terms (awó, "grandfather")

Switch-reference

Koasati has switch-reference marking, in which suffixes indicate whether the subjects of two verbs are co-referent. The suffix –k indicates that the subject of the verb that follows is the same as that of the previous verb, while –n indicates that the subject is different than that of the previous verb. The suffixes –ok and –on can also be used in the same way for extra emphasis or "focus". The switch-reference marker –p indicates the introduction of a new topic. An example of each suffix follows:

• nó꞉ra-k ɫabósli-h bánna-k hí꞉ca-t á꞉ta-toho-꞉li-k akkámmi-tik labósl-á꞉ha-k sam, kí,꞉c-o-t — "Nora tried to extinguish it, and she kept on watching it, but this being so, she was unable to extinguish it."
• athómma-k yomáhli-n calakkí ho-ká꞉ha-hco-k — "They called the wandering Indians Cherokees."
• skólka im-alo, kí, st-o-n mí꞉ta-k im-alósti-tika-p — "They were not interested in school; however, others were interested in it."