Q: Here goes … effective vs. effectual vs. efficacious. Any difference?
A: The adjectives “effective,” “effectual,” and “efficacious” have the same primary meaning: producing or capable of producing a desired effect.
When used in that sense, the only reason for picking one over the others is style. The best one is the one that goes best with the sentence you’re writing.
The American Heritage Dictionary of the English Language (5th ed.) gives these examples of the three words used in this sense: “an effective reprimand; an effectual complaint; an efficacious remedy.”
All three adjectives are derived from efficere, a Latin verb meaning to work out or bring about, according to the Chambers Dictionary of Etymology. The Latin word, a compound, was formed from ex (out) and facere (to make or do).
The adjectives “effective” and “effectual” showed up in English in the late 1300s, while “efficacious” appeared in the early 1500s.
The earliest examples of both “effective” and “effectual” in the Oxford English Dictionary are from John Trevisa’s 1398 translation of De Proprietatibus Rerum (On the Properties of Things), a medieval encyclopedia by Bartholomaeus Anglicus:
Effective: “Oleum iuniperinum [sic] … is most effectif ayeins the quartayne.”
Effectual: “The more white and bryght that he [a pearl] is, the more effectuel and vertuouse [L. efficacior] it is holde.”
(We’ve changed the runic letters thorn to “th” and yogh to “y.”)
The earliest example of “efficacious” in the OED is from the evangelical author William Roy’s Satire Against Cardinal Wolsey (1528): “Goddis worde is so efficacious.”
Why do we have three similar adjectives with the same primary meaning and the same Latin source?
Because the three words entered English by way of three different Old French words: effectif, effectuel, and efficacité, according to Chambers.
Interestingly, “effectual” and “efficacious” have only the primary meaning we’ve been discussing (producing or capable of producing a desired effect).
However, “effective” can also mean operative (“The ordinance will be effective in 15 days”), actual (“Inflation led to an effective drop in the value of the dollar”), and ready for action (“The Marines have no effective presence in the area”).
Finally, efficere, the Latin verb that gave us all three adjectives, is also the source of the “feck” in “feckless.”
As we wrote on our blog in 2011, “feck” originated as an early 15th-century Scottish abbreviation of “effect.”
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