Siouan languages and most of all the Degiha-branch languages feature a rich classificatory system based on positional markers. Different stages of grammaticalization can be observed within this system; according to Rankin (2004:202) positional verb roots for 'sit, stand, lie' in Degiha morphosyntax "have yielded deictic classifiers, locative classifiers, interrogative classifiers, new sets of aspectual auxiliaries and new causative verbs of placing, all using the definite articles as roots. In Omaha, Ponca and Quapaw, homophony has caused reanalysis of an evidential particle as a positional article, giving rise to the use of certain of the positional articles as evidential classifiers and even evidential verb stems".
As Rankin posits, the positional stative verbs 'be sitting, be standing, be lying' are inherently continuative by semantics and are predestined for an aspectual function.
Santee Dakota (Santee-Sisseton)
In Santee Dakota (Dakotan, Mississippy Valley Siouan) yąké 'sit' is usually employed for continuative aspect. According to Rankin, the other two positionals for 'stand' and 'lie' can also be used in this function, but that involves pragmatic marking. If the subject of the verb is unequivocally defined as being in a certain posture and that posture is in focus, then any positional may be used as continuative auxiliary, otherwise the 'sit' positional is the auxiliary marking for position and continuative aspect. In example (1) no posture of badger is defined, thus the 'sit' positional is used and it functions as a continuative marker and the positional meaning is ignored. In example (2) the verb 'hang' clearly defines a posture for the bow which is also in focus, therefore again yɑ̃ké 'sit' is employed as a continuative marker, and the listener will not think that the bow sits, but will understand that the bow was continuously hanging.
(1) xóka hečhú̃ yɑ̃ké čʔa wɑ̃na wašéča xĩča badger thus.do he.sit and now rich very 'Badger became very rich doing this (i.e. hunting in this way).' [Riggs 1893:95 by Rankin 2004:204] (2) ú̃khɑ̃ čháɣa itázipa wɑ̃ otkeya yɑ̃ké then ice bow a hang it.sit 'Hanging there was a bow of ice.' [RIGGS 1893:88 by Rankin 2004]
If the used positional contradicts the posture of the subject defined by the verb or if the verb subjects posture is not in focus (de-emphasized), it may function as a pragmatic modifier, as in the example below, where the speaker skilfully expresses "that Unktomi, the trickser, is slinking along, rather than walking upright". (Rankin 2004:204)
(3) ũktómi wã kakhen yá wãká; mdé wã kahda yá wãká ... Unktomi a thus he.go he.lie lake a beside he.go he.lie 'Unktomi was going along; he was going beside a lake ...' [Riggs 1893:87 by Rankin 2004]
According to Rankin, in Lakhota the original 'standing' positional hã has become the standard continuative marker and is thus completely grammaticalized, see example (5). hã may be used along with positional verbs depicting other postures, including 'sit' and 'lie'. In the strange example (5), "hã is the continuative enclitic for íotaka, and yãka, etymologically the older, common Siouan verb 'sit', functions in a locative/clasificatory role". (Rankin 2004:205)
(4) iktó kákhena íčimani-ya hã Ikto yonder make.journey.go stand 'Ikto was starting off on a journey ...' (5) íotaka hã yãka he.sit stand sit 'Sitting he sits.' (6) xpáya-he 3.lie-stand (-he is a morphophonologically modified variant of hã 'stand') 'he was standing' (lit. 'he stands sitting')
(Lakhota examples from Deloria 1932, by Rankin)
Nakota (Yankton / Assiniboine)
Rankin states that according to Deloria, Nakota employs yãká 'sit' as continuative marker, like Santee. Wherever yãká 'sit' is used, continued action is expressed.
(7) nážĩ yãká 3.stand sit 'he was standing' (lit. 'he stands sitting') (Deloria 1932:165, by Rankin)
In this example, yãká 'sit' functions as a continuative marker and its original 'sitting posture' meaning is lost, similarly to Lakhota hã 'stand'.