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Why a black swan is a rara avis

Q: Lately I have seen several references to “black swan” meaning an unexpected event or an anomaly. Is this new or just new to me? I can guess how it originated but would love to hear from you about it.

A: The use of the phrase “black swan” to mean a rare or unexpected occurrence ultimately comes from a passage in the Satires of the Roman poet  Juvenal. The Latin passage is also the source of another English term for a rarity, “rara avis.”

In Satire VI,  Juvenal describes a wife with what he considers all the right qualities—looks, charm, money, fertility, and ancestry—as “rara avis in terris nigroque simillima cygno” (“a bird rare on earth and similar to a black swan”).

When Juvenal was writing in the late first and early second centuries, Romans believed that all swans were white, so a black swan would have been an impossibility. We know now, though, that black swans (at least mostly black ones) do indeed exist. More on this later.

When the phrase “black swan” first showed up in Middle English, according to the Oxford English Dictionary, it was used in contrast to emphasize the whiteness of the European swan:

“The swan hatte signus in latyn and olor in grew [Greek] for he is al white in fetheres, for no man findiþ [findeth] a blak swan.” (From John Trevisa’s translation in the late 1300s of De Proprietatibus Rerum, an encyclopedic Latin reference compiled in the mid-1200s by the medieval scholar Bartholomeus Anglicus.)

In the 16th century, the OED says, the usage took on the sense of “something extremely rare (or non-existent); a rarity, rara avis.”

The dictionary’s first citation is from a sermon denouncing sensuality: “Captaine Cornelius is a blacke Swan in this generation.” (Earlier, the virtuous captain’s deeds are praised as “musicke to God.”) From a sermon on Easter Tuesday, 1570, by Thomas Drant at St. Mary Spital, a priory and hospital (lodging for travelers) in Spitalfields, London.

The next Oxford example is from a play that satirizes the theater: “The abuse of such places [ancient Roman theaters] was so great, that for any chaste liuer [liver] to haunt them, was a black swan, & a white crow” (from Schoole of Abuse, 1579, by Stephen Gosson).

In the late 17th century the term “black swan” appeared literally, in reference to Cygnus atratus, a swan that’s native to Australia. It’s mostly black, with a red bill and some white wing feathers.

The OED’s earliest citation is from a 1698 report in the Philosophical Transactions of the Royal Society: “Black Swans, Parrots and many Sea-Cows were found there.” The sightings were in Australia, known at the time as Hollandia Nova, New Holland, or Nieuw Holland, a usage introduced by the Dutch seafarer Abel Tasman in 1644.

As for “rara avis,” when the phrase appeared in English in the early 17th century it meant “a person of a type rarely encountered; an unusual or exceptional person; a paragon,”  according to the dictionary.

The first Oxford example is from The Miseries of Enforced Marriage, a 1607 play George Wilkins: “And by that, thou hast beene married but three weekes, tho thou shouldst wed a Cynthia rara avis, thou wouldest be a man monstrous: A cuckold, a cuckold.”

In the mid-17th century, the phrase came to mean “that which is seldom found, a rarity; an unusual, exceptional, or remarkable occurrence or thing.”

The earliest OED example is from a 1651 issue of the Faithfull Scout, a London weekly:  “Moderation, which may well be intituled the Rara avis of these times.”

Today, according to Merriam-Webster Unabridged, “rara avis” means “a rare person or thing.” The dictionary gives this example from the Atlantic: “that rara avis of politics, a disinterested man.”

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