Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
sufficiently (adv.)
When this adverb modifies an adjective, the construction is usually followed by an infinitive: Turnout of our party’s voters was sufficiently high to guarantee victory. Some people have argued that following the construction with a that clause instead of an infinitive is not Standard English. If this was once true, it is true no longer: Turnout of our party’s voters was sufficiently high that we knew we’d win is now Standard. Note too that, like the adjective sufficient, the adverb sufficiently may sometimes sound over-Formal: was high enough may be enough.
