Get a grip, Muldoon.
Dear Word Detective: I’ve been trying to find any differences in the connotations of “capricious” and “mercurial.” They both deal with inconsistencies, but the only difference seems to be in their etymology: “capricious” started with the inconsistencies of goats, whereas “mercurial” started with the inconsistencies of the god Mercury. Is there anything more to these two words’ meanings? — Danielle Then.
That’s an interesting question. Say, do you mind if I borrow “The Inconsistencies of Goats” for the title of my next book? Usually I’d think of one myself, but all these goats are driving me crazy. I’ve tried to convince them they’d be happier outside, but they get halfway out the door and change their minds. Aside from a touch of agoraphobia, however, goats are just about the coolest animals going, much cooler than sheep, who are, let’s be blunt, total idiots. Goats are actually a lot like cats. Except for the horns, of course. I’m glad cats don’t have horns, aren’t you? Oh yeah, you had a question.
“Capricious,” which today we use to mean “impulsive,” “unpredictable” and, therefore, “unreliable,” is, appropriately, a word with a somewhat convoluted history. The noun behind the adjective “capricious” is “caprice,” meaning “whim, impulse, sudden urge or unusual action.” English borrowed our “caprice” in the 17th century from the French, who had adapted the Italian “capriccio,” also meaning “whim,” etc. But the earlier and original meaning of the Italian word was not “whim,” but “sudden shock” or “horror.” And the animal behind the word was not a goat, but a hedgehog. The Italian word is thought to be a blend of “caput” (head) with “riggio” (hedgehog), describing a person whose hair was standing on end, like a hedgehog’s, from fright or surprise. When “capriccio” eventually lightened up in Italian and came to mean “playful, whimsical,” the fact that it resembled the Italian word “capro” (goat) led people to associate the frisky play of young goats with “capriciousness,” which made much more sense than trying to rationalize “friskiness” with the torpid behavior of hedgehogs.
“Mercurial,” meaning “lively, volatile, given to quick changes of mood,” does indeed hark back to the Roman god Mercury (who was based on the Greek god Hermes), messenger of the gods and a notably fleet fellow (due in part to his winged shoes). Interestingly, Mercury was also the god of trade and travel, and his name comes from the Latin “merx,” meaning (and the root of) “merchandise.” “Mercury” today is best known as the name of a planet, an element, and a brand of car made, until 2011, by Ford. The adjective “mercurial,” which first appeared in English in the 14th century, can refer to anything having anything do do with Mercury, from the planet to the element, various plants, and medicines containing the element. The use of “mercurial” to mean “highly changeable” in reference to people dates to the mid-17th century and was apparently originally a reference to the fickle personality of the god Mercury. The modern use of “mercurial,” however, is more a reference to the metallic form of mercury (also known as “quicksilver”), which is the only metal which is liquid at room temperature. Apart from being extremely toxic, mercury is known for its highly fluid and quick movement, which is what makes it a good metaphor for swift change and unpredictability.
Every thesaurus I’ve checked considers “capricious” and “mercurial” to be synonyms, but I think there is a slight difference between the two. To describe someone as “mercurial” is not necessarily at all derogatory. Great artists and similar sensitive types are often lively, impulsive and given to “quicksilver” changes of mood. But to describe someone as “capricious” marks the person as undependable, flighty, and possibly petty, likely to disregard the effect of a sudden change in plans, etc., on other people. It’s not a distinction that can be traced to etymology or the broad definitions of the words, but I do think “mercurial” and “capricious” have developed that shade of difference in modern usage.