Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
plenty (adv., adj., n., intensifier)
Most of plenty’s problems are in the spoken language; in Standard writing it lives a much straitened life, mostly as a noun, which causes no trouble: They had plenty of money. October is a season of plenty.
As a predicate adjective, as in Starlings surely are plenty these days, plenty rarely occurs today in the written language, but it does occur in Conversational—especially Casual—English. As an attributive adjective, as in We had plenty money in those days, it looks odd and is Nonstandard in print but occurs frequently in Conversational contexts, especially at the Casual level. Right alongside it, however, and unquestionably Standard at all levels are the use of plentiful instead of plenty in predicate adjective functions (starlings are plentiful) and the insertion of of between plenty and the noun instead of using plenty as an attributive (plenty of money).
As an adverb, plenty is used most often as an intensive, as in They were plenty angry, and as a full adverb, as in I’ve exercised plenty today. But these uses too are limited to speech, mainly Casual and Impromptu levels. And the use of plenty with more also is for Conversational English only, where it is Standard, both when more behaves like a noun, as in We got plenty more yesterday, and when plenty seems to be an intensifier, as in We got plenty more calls.
