What does facultatively mean?
"Facultatively" is a formal adverb describing something done by option rather than obligation. It derives from the same root as "faculty" — Latin facultas, meaning capability or ease — and carries the sense of a capacity that may be exercised or withheld. In everyday academic writing, it signals that a step, requirement, or activity is discretionary: one might write that a course component is facultatively available to advanced students. The word's most vigorous modern life, however, is in biology. Microbiologists use it to describe organisms that can operate under alternative conditions, most famously "facultatively anaerobic" bacteria, which generate energy with oxygen when it is present and switch to fermentation when it is not. Because it is technical and slightly cumbersome, "facultatively" rarely appears in casual speech; "optionally" or "at one's discretion" usually serves instead. Yet within its specialist niches it is precise, well-established, and indispensable.
In an optional or non-obligatory manner; by choice rather than necessity.
"The final module is facultatively offered to students who wish to specialize further."
Formal register; "optionally" is preferred in general writing.
In biology, in a manner characterized by the ability to function under two different sets of conditions, such as with or without oxygen.
"Staphylococcus aureus grows facultatively, tolerating both oxygen-rich and oxygen-poor environments."
Biologists can't stop saying it: the bacteria in your gut are 'facultatively anaerobic' — happy with oxygen, happy without. Few adverbs get such steady scientific employment.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of facultatively
"Facultatively" traces back through the adjective "facultative" to Latin facultas, meaning "capability," "ease," or "opportunity," itself from facilis ("easy"), the root of English "facility." The adjective entered English in the early 17th century, with the adverb following soon after. Cognates from the same Latin stock include "faculty," "facile," and "facilitate."
Related word forms
How facultatively is actually used
Predominantly formal and technical. Outside academic prose it sounds stilted, where "optionally" is more natural. Its most frequent modern habitat is microbiology, particularly in descriptions like "facultatively anaerobic."
Easily confused with facultatively
"Facetiously" means jokingly or flippantly, while "facultatively" means optionally or in a non-obligatory way; the two share a similar rhythm and ending but nothing else.