a single fortunate event doesn’t mean that what follows will also be good
The annual migration of swallows to Europe from southern climes at the end of winter was the subject of a proverb in Ancient Greece: μία χελιδὼν ἔαρ οὐ ποιεῖ, in which ἔαρ means spring; it is found in Nicomachean Ethics, by the philosopher and scientist Aristotle (384-322 BC), who did not interpret it as we do (see footnote):
translation (1926): Harris Rackham (1868-1944)
To be happy takes a complete lifetime; for one swallow does not make spring, nor does one fine day; and similarly one day or a brief period of happiness does not make a man supremely blessed and happy.
The basic metaphor is that the end of winter is the end of hard times, but that more than one piece of evidence is needed to prove that it has been reached.
The English proverb is first recorded in 1539: in Prouerbes or adagies with newe addicions gathered out of the Chiliades of Erasmus, an adaptation of Adagiorum chiliades (Thousands of proverbs) by the Dutch humanist and scholar Desiderius Erasmus (circa 1469-1536), Richard Taverner (circa 1505–1575), translator and evangelical reformer, wrote:
Vna hirundo non facit ver¹.
It is not one swalowe that bryngeth in somer. It is not one good qualitie that maketh a mā [= man] good². Swalowes be a token of the begynnynge of somer, yet one swalowe is no sure token. So of al other thynges.
¹ Latin ver means spring; aestas means summer.
² see footnote
The English playwright and epigrammatist John Heywood (circa 1496-circa 1578) also recorded the proverb in A dialogue conteinyng the nomber in effect of all the prouerbes in the englishe tongue compacte in a matter concernyng two maner of mariages (1546):
One swalow maketh not sommer.
But in A Collection of English Proverbs (1678), John Ray (1627-1705) recorded the following:
One swallow makes not a spring, nor one woodcock a winter.
The earliest English versions of the proverb have summer and not spring probably because the former word, which goes back to Old English, was used in contradistinction to winter to denote the warmer half of the year. The expression summer and winter, also winter and summer, was used to mean all the year round. The noun spring in the sense of the season between winter and summer is first attested in the mid-16th century and is apparently from the spring of the year, in which spring meant the time of springing into existence. Similarly, for example, the spring of the leaf denoted the time when trees begin to burst into leaf again, and the spring of the moon meant the increase of the moon. The original sense of the noun spring, attested in the early 9th century, is the place where water wells up from an underground source, hence the figurative sense the origin of something.
In the Italian and French versions of the proverb, the season is spring:
– una rondine non fa primavera
– une hirondelle ne fait pas le printemps
But in the Spanish and German versions, it is summer:
– una golondrina no hace verano
– eine Schwalbe macht noch keinen Sommer
from The Adages of Erasmus: Selected by William Barker (2001):
One swallow does not make a summer³.
Μία χελιδὼν ἔαρ οὐ ποιεῖ, A single swallow does not make a summer, meaning that one day is not time enough to acquire virtue or education. Or that one thing well done or well said is not sufficient to earn you the reputation of a good man or a good speaker, for many good qualities go to make this up. Or that to obtain certainty on some question, one single theory is not enough. If a great many approaches lead to the same result, then and then only will your theory be acceptable. It can so easily happen that one swallow should appear early by mere chance. This is derived from the natural habits of the swallow, which is the herald of early summer, for it flies away when winter comes. Whence Horace’s phrase ‘When Zephyrs blow and swallows first appear’, which refers to the early summer. Aristotle in the first book of the Ethics: ‘One swallow makes no summer, nor does one day’; and in the same way it takes more than one day or one short space of time to make a happy man. Aristophanes in the Birds: ‘He seems to me to need full many swallows’, where the scholiast sees a reference to the proverb I have just recorded, One swallow does not make a summer. There is something akin in Sophocles’ Antigone: ‘What one man owns can never make a city’. For just as one swallow does not make a summer, so one man does not make a commonwealth nor one coin a rich man.
Una hirundo non facit ver
Μία χελιδὼν ἔαρ οὐ ποιεῖ, id est Unica hirundo non efficit ver, hoc est unus dies non sat est ad parandam virtutem aut eruditionem. Aut non unum aliquod benefactum benedictumve sufficit ad hoc, ut viri boni aut boni oratoris cognomen promerearis; plurimis enim virtutibus ea res constat. Aut ut certum aliquid cognoscas, non satis est unica coniectura. Quod si permultae conveniant, tum denique probabilis fuerit coniectura. Siquidem fieri potest, ut una quaepiam hirundo casu maturius appareat. Sumptum ab hirundinis natura, quae veris est nuntia; nam hyeme devolat. Unde Horatius: Zephyris et hirundine prima, de primo vere sentiens. Aristoteles libro Moralium primo: Σὸ γὰρ ἔαρ οὔτε μία χελιδὼν ποιεῖ οὔτε μία ἡμέρα, id est Ver enim nec una hirundo facit nec unus dies. Et beatum eodem modo felicemve nec unus dies nec breve efficit tempus. Aristophanes in Avibus: Δεῖσθαι δ’ ἔοικεν οὐκ ὀλίγων χελιδόνων, id est Multa videtur opus habere hirundine. Interpres indicat allusum ad proverbium, quod modo retulimus: Μία χελιδὼν ἔαρ οὐ ποιεῖ. Huic affine videtur illud Sophocleon in Antigona: Πόλις γὰρ οὐκ ἔσθ’ ἥτις ἀνδρός ἐσθ’ ἑνός, id est Namque unius quae sit viri haud est civitas. Etenim quemadmodum una hirundo non facit ver, ita nec unus homo facit civitatem nec unus nummus divitem.
³ But Erasmus uses ver, meaning spring.