Feasible comes from faire, the French verb meaning “to do.” Doable and feasible therefore originally meant literally the same thing: “capable of being done.” Indeed, doable was formed with -able, the Latin-derived French ending meaning “capable of” combined, in this instance, with do, a word with roots in Old English and one of the most basic and useful of our verbs. Though their respective etymological meanings may overlap, doable and feasible exist more in parallel with each other than as true synonyms. As with most such pairs of words, the Latin-derived term is used when describing more abstract notions. The words most commonly modified by feasible include:
These are words that describe what has yet to be decided or what will be carefully considered. By contrast, doable modifies more concrete terms:
Feasible is used when an element of abstraction, distance, and technical specificity is needed. The more earthy doable is rarely used in formal writing, and is not found in the works of Shakespeare, the King James Bible, or any of the founding documents of the United States.
This abstract use of feasible also accounts for the word that expresses a putative, conceptual, or hypothetical state: feasibility. Indeed, we frequently encounter “feasibility study” but not “doability study” (although doability is a word that is sometimes used, it hasn’t yet been added to most dictionaries). As long as something is just an idea, it’s feasible. When it’s time for action, we need to find out if it’s doable.