Effective, Efficient, Effectual, and Efficacious

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My recent post on cost-effective and cost-efficient garnered a couple of emails from readers who suggested that I might not be aware that effective and efficient have different meanings.

Despite the difference between the words effective and efficient when used alone, once the word cost is added to them to produce cost-effective and cost-efficient, the meaning of both compounds appears to be economical or cost-saving. I’d welcome the input of an economist who could provide contexts to show a difference in meaning between the compounds, if one in fact exists.

Effective and efficient, on the other hand, belong to a group of adjectives relating to the idea of getting results. Their similarity in meaning is clear in these OED definitions:

effective: Powerful in effect; producing a notable effect; effectual.

efficient: Productive of effects; effective; adequately operative.

effectual: That produces its intended effect, or adequately answers its purpose.

efficacious: That produces, or is certain to produce, the intended or appropriate effect; effective.

Like the readers who wrote to me, I see a significant difference between effective and efficient. I understand efficient to mean, “marked by ability to choose and use the most effective and least wasteful means of doing a task or accomplishing a purpose.” For example, burning the house down to get rid of termites would be effective, but not efficient.

Here are some examples of suggested usage based on a note in the Oxford American Writer’s Thesaurus:

Use effective to describe something that produces a definite effect or result.

Antony proved that he was an effective speaker by rousing the rabble against the men who killed Caesar.

Use efficient when the intention is to imply skill and economy of energy in producing the desired result.

In less than a year, the new treasurer’s efficient management resulted in the elimination of the organization’s enormous debt.

Use effectual to describe something that produces the desired result in a decisive manner.

Destroying the bridge proved to be an effectual strategy for stopping the invaders.

Use efficacious to describe something that produces the desired effect.

Ginger is an efficacious remedy for an upset stomach.

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7 thoughts on “Effective, Efficient, Effectual, and Efficacious”

  1. The OED definition for efficient seem oddly inappropriate if not downright incorrect: “efficient: Productive of effects; effective; adequately operative. “ Nonsense. In American English, at least, efficient most definitely implies “skill and economy of energy in producing the desired result” and is not synonymous with effective.
    Effective, efficacious, and effectual all seem to be, literally, synonymous judging by their stated definitions. No tangible distinctions are made. The impression I get is that efficacious and effectual are phony-isms, akin to instinctual, normalcy, legitimize and empathetic. Assemblages that “seem like” they should be real words but are in fact of questionable provenance and in any case, entirely unneeded.

  2. @Maeve: Once again you hit the nail on the head 🙂
    @venqax and Precise Edit: Agreed, but is there a need to set limits on how many words we have in our language? It’s helpful to have some extra synonyms available so that we can change things up once in a while.

  3. It’s often fun to use elegant instead of efficient. It’s sometimes even appropriate, although perhaps you risk sounding affected. As for the others, I prefer effective, its relatives being less elegant.

  4. I worked in the American pharmaceutical industry, and there they make a distinction between “effective” and “efficacious”.

    A medication is “effective” if it is very likely to produce the desired result when it is used as directed.
    An “efficacious” medicine is that as well, but it is also something that is likely to actually BE used as directed.

    By example, a skin medication that you must apply every four hours for a week might be very effective, but it would not be considered efficacious, as most people would not follow those directions completely.

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