Klamath is a member of the Plateau Penutianlanguage family, which is in turn a branch of the proposed Penutian language family. Like other proposed Penutian languages, Plateau Penutian languages are rich in ablaut, much like Indo-European and Afro-Asiatic languages. Further evidence for this classification includes some consonant correspondences between Klamath and other alleged Penutian languages. For example, the Proto-Yokutsretroflexes*/ʈ ʈʼ/ correspond to Klamath /tʃ tʃʼ/, and the Proto-Yokuts dentals*/t̪ t̪ʰ t̪ʼ/ correspond to the Klamath alveolars/t tʰ tʼ/.
Most consonants can be geminated. The fricative /s/ is an exception, and there is evidence suggesting this is a consequence of a recent sound change.Albert Samuel Gatschet recorded geminated /sː/ in the late 19th century, but this sound was consistently recorded as degeminated /s/ by M. A. R. Barker in the 1960s. Sometime after Gatschet recorded the language and before Barker did the same, */sː/ may have degeminated into /s/.
Klamath word order is conditioned by pragmatics. There is no clearly defined verb phrase or noun phrase. Alignment is nominative–accusative, with nominal case marking also distinguishing adjectives from nouns. Many verbs obligatorily classify an absolutive case. There are directive and applicative constructions.
Rude, Noel (1987). Some Sahaptian-Klamath grammatical correspondences. Kansas Working Papers in Linguistics, 12:67-83.
Rude, Noel (1988). Semantic and pragmatic objects in Klamath. In In Honor of Mary Haas: From the Haas Festival Conference on Native American Linguistics, ed. by William Shipley, pp. 651–73. Berlin: Mouton de Gruyter.
Rude, Noel (1991). Verbs to promotional suffixes in Sahaptian and Klamath. In Approaches to Grammaticalization, ed. by Elizabeth C. Traugott and Bernd Heine. Typological Studies in Language 19:185-199. New York and Amsterdam: John Benjamins Publishing Company.