Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
ineffective, ineffectual, inefficacious (adjs.)
These are synonyms meaning “not able to produce the needed result”: All the treatments proved ineffective [ineffectual, inefficacious]. Ineffective and ineffectual, when applied to a person, differ somewhat: ineffective is a relatively matter-of-fact report on a current lack of success; ineffectual implies an ingrained inability to succeed, in the past and probably in the future as well. Inefficacious is a relatively low frequency, pretentious word that has one more syllable than ineffective but not much else. See EFFECTIVE.
