Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
these kind of, these sort of
American English insists that all levels of the written language and nearly all levels of the spoken except Casual and Intimate use this or that with singular kind or sort and follow them with of plus a singular noun; all levels also use these or those only with plural kinds or sorts and follow them with of plus a plural noun: this kind [sort] of dog; those kinds [sorts] of dogs. Common English is much less worried about mixing the numbers of the three variables in these constructions, and British English is too. But for many Standard-using Americans, failures on these structures are powerful shibboleths. See KIND.
