“It is a truism that people speak ‘loosely’- that is, that they often say things that we can recognize not to be true, but which come close enough to the truth for practical purposes.”
– explained Professor Peter Nathan Lasersohn (University of Illinois, Dept. of Linguistics) in a 1999 paper for the journal Language, 75 (3): pp.522-551 which carried the first account of ‘Pragmatic Halos’ and their everyday uses.
For a more recent and specific examination of ‘kinda’ and ‘sorta’ – in the Lasersohnian sense, see: Inherent and coerced gradability across categories: manipulating pragmatic halos with sorta, Curt Anderson, Proceedings of SALT 23. (2013)
If, however, you’d like a less colloquial approach, looking at ‘kind of’ and ‘sort of’ instead of ‘kinda’ and ‘sorta’, then see : This is kind of / sort of interesting: variation in hedging in English, Stefan Th. Gries, and Caroline V. David, Towards multimedia in corpus linguistics, 2007.
[ Research research by Martin Gardiner ]