The noun serendipity denotes the faculty of making by accident discoveries that are both fortunate and unexpected.

(It has been borrowed into Spanish as serendipia, into Italian as serendipità, and into French as sérendipité.)

It was coined by the English writer and politician Horace Walpole (1717-97). In a letter that he wrote to his friend Horace Mann on 28^th January 1754, he explained:

(edited by Peter Cunningham – published by Henry G. Bohn, London, 1861)
I must tell you a critical discovery of mine àpropos [= à propos, by the way]: in an old book of Venetian arms, there are two coats of Capello, who from their name bear a hat; on one of them is added a fleur-de-lis on a blue ball, which I am persuaded was given to the family by the Great Duke, in consideration of this alliance; the Medicis, you know, bore such a badge at the top of their own arms. This discovery I made by a talisman, which Mr. Chute calls the Sortes Walpolianæ, by which I find every thing I want, à pointe nommée [= à point nommé, just when needed], wherever I dip for it. This discovery, indeed, is almost of that kind which I call Serendipity, a very expressive word, which, as I have nothing better to tell you, I shall endeavour to explain to you: you will understand it better by the derivation than by the definition. I once read a silly fairy tale, called “The Three Princes of Serendip:” as their Highnesses travelled, they were always making discoveries, by accidents and sagacity, of things which they were not in quest of: for instance, one of them discovered that a mule blind of the right eye had travelled the same road lately, because the grass was eaten only on the left side, where it was worse than on the right—now do you understand Serendipity? One of the most remarkable instances of this accidental sagacity, (for you must observe that no discovery of a thing you are looking for comes under this description,) was of my Lord Shaftsbury, who, happening to dine at Lord Chancellor Clarendon’s, found out the marriage of the Duke of York and Mrs. Hyde, by the respect with which her mother treated her at table. I will send you the inscription in my next letter; you see I endeavour to grace your present as it deserves.

(The mule mentioned by Walpole was actually a camel in the story.)

Serendip derives from Sarandīb, the Arabic name for Ceylon, now Sri Lanka. Apparently, this Arabic name is from Sanskrit Simhala-dvīpa, from simha, lion, and dvīpa, island.

The “silly fairy tale” that Walpole refers to was printed in London in 1722 with the title The Travels and Adventures of Three Princes of Sarendip. Inter-mixed with Eight Delightful and Entertaining Novels. Translated from the Persian into French, and from thence done into English. Through a 1719 French translation by de Mailly, the source is the 1557 Venetian book Peregrinaggio di tre giovani figlivoli del Re di Serendippo by Cristoforo Armeno, whose inspiration was the Hast Bihist of the Persian writer of the late 13^th and early 14^th century Amir Khosrau.

(Incidentally, a very free French translation of Cristoforo Armeno’s book by Simon Gueulette in 1712 was used by the French writer Voltaire (François-Marie Arouet – 1694-1778) for Zadig ou la destinée (1747).)

The following, from The Evening Telegraph (Dundee, Scotland) of 22^nd June 1877, is a misinterpretation of serendipity, since Walpole wrote, about “accidental sagacity”, that “no discovery of a thing you are looking for comes under this description”:

Luck and Serendipity.—It is clear enough that serendipity is a very different thing from mere ordinary luck. We call a man lucky, for example, who escapes unhurt in a railway accident, or in the explosion of his domestic boiler, or when a run-up house in a new quarter falls upon him; in short, a man is lucky who evades any of the numerous perils with which mechanical science has enriched daily life. But this sort of good fortune is quite distinct from serendipity. Take another kind of luck. We call the man lucky who is always meeting with chance gifts of fortune. The old lady whom he rescues from a yelping poodle leaves him an estate; he cannot enter his name in a club lottery without winning the sweep-stakes; all ordinary things go well with him, and extraordinary hazards fall out, as if by special arrangement or pre-established harmony, for his comfort and well-being. But serendipity is entirely distinct from this favouritism of fortune. The mere lucky man gets things without looking for them or thinking of them; the man with serendipity has to be grateful for much smaller favours, but then they are the favours which he happens particularly to want. Take the instance which Walpole seems to have had especially in his mind. Two men may be in doubt about a reference in a book—a reference which it is necessary for their work or for their mental satisfaction that they should find. Give one of them indexes without number, as indexes have always been in this imperfect world, and he will labour in vain, and search for hours with no result but loss of time and temper. The other, the man with serendipity, has only to take up the first volume that lies near his hand, or even by chance to look at a newspaper, and what he wants or a clue to what he wants leaps to his eyes. Serendipity is not confined, of course, to a happy knack of hitting on the right page of a book at the right time, though even this is no small boon, as people who lack it will confess. In all the minor matters of life the gift has its power, and the owner of the gift falls in with just what he has begun to wish for, and would soon have begun to look for. If he has set his heart on any out-of-the-way possession—a rare old book, a particular piece of antiquated furniture, a park hack of unusual acquirements, a house in the country within easy reach of town—the desirable thing falls, as it were, into his lap. The first bookstall he passes has the rare volume; a broker in a back-street where he has lost his way happens to display the carved chest; the man who dines at the next table to him at the Club is parting with the horse, or wants to let the house. The inheritors of the luck of the Prince of Serendip save a small fortune in advertisements, and a world of trouble in running up and down in search of what they need. In ladies the gift takes the shape of securing at the first venture servants and governesses who are “treasures,” and who get married just in time to prevent them from becoming old family retainers of the tedious and trying kind.

In The New York Times (New York, N. Y.) of 29^th April 1905, Emma Carleton reviewed an essay on serendipity, by Ellen Burns Sherman, that had been published in the April issue of The Criterion. In this review, titled Serendipity. The Difference Between “Coincidental Sagacity” and the “Accidental Sagacity” Defined and Named by Horace Walpole, Emma Carleton distinguished between what she called “coincidental sagacity”, denoting “success in a quest”, and Horace Walpole

brand of “accidental sagacity.” According to the Walpole theory, the thing discovered must not have previously occupied the man of the discoverer, or the “serendipper,” as it were.

At the same time, Emma Carleton coined the noun serendipper, denoting a person possessing the faculty of making by accident discoveries that are both fortunate and unexpected. This noun has been exclusively used in the USA; in The Sphere (London) of 10^th June 1905, the literary columnist, who had read The New York Times, was right, since he wrote:

I trust that a form of the word one sees in the American newspapers, “serendipper,” may not reach this country.

The equivalent British word, serendipitist, was coined, or first used, by the Irish writer James Joyce (1882-1941) in Finnegans Wake (1939):

You (will you for the laugh of Scheekspair just help mine with the epithet?) semisemitic serendipitist, you (thanks, I think that describes you) Europasianised Afferyank!

The Italian-born microbiologist Salvador E. Luria (1912-91), of the University of Illinois, gave his own definition of serendipity in the following article, published in Scientific American of April 1955:

The T2 Mystery

T2 is a virus which dissolves bacteria. Normally its attack is followed by the appearance of a generation of new viruses. But sometimes the viruses appear to be missing. Why?

Our story has as its critical episode one of those coincidences that show how discovery often depends on chance, or rather on what has been called “serendipity”—the chance observation falling on a receptive eye. The episode is a good illustration of the principle of “controlled sloppiness,” which states that it often pays to do somewhat untidy experiments, provided one is aware of the element of untidiness. In this way unexpected results, sometimes real discoveries, have a chance to come up. When they do, we can trace their cause to the untidy, but known, features of the experiment.