Q: What’s the scoop on “optimal” vs. “optimum”? The company I work for says its technology is designed “to maintain the optimal temperature.” To my ear “optimal” is correct, but our chief scientist, a Brit, prefers “optimum.” Are they interchangeable?
A: As adjectives, “optimum” and “optimal” mean the same thing: most favorable, advantageous, desirable.
“Optimum,” which is also a noun, is the older word. It was borrowed directly from Latin (optimum: the best), and entered English as a noun in the mid-19th century.
The earliest published reference in the Oxford English Dictionary (from 1848) describes the cultivation of mulberry to reach “its maximum of extent and its optimum of quality.”
The word was first used as an adjective in an 1885 work that discusses the “optimum point” at which plant life “is carried on with the greatest activity.”
“Optimal” was formed from “optimum” and entered English in 1890. Again, the first OED citation comes from scientific writing: “There is probably an optimal temperature, or one at which the process proceeds most rapidly or most favourably.”
Both words have been used as adjectives up to the present time. In my opinion, it’s a toss-up. Use either one.
But here’s another opinion. Bryan A. Garner, in Garner’s Modern American Usage
“It serves the principle of differentiation to distinguish between the two forms,” he writes. He adds, however, that the adjective “optimum” is edging out “optimal” in popularity.
In the end, public opinion will choose the winner.
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