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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.

[μία γὰρ χελιδὼν ἔαρ οὐ ποιεῖ, οὐδὲ μία ἡμέρα: οὕτω δὲ οὐδὲ μακάριον καὶ εὐδαίμονα]

Aristotle (384-322 BC) Greek philosopher

Nicomachean Ethics [Ἠθικὰ Νικομάχεια], Book 1, ch. 7 (1.7, 1098a.18) (c. 325 BC) [tr. Rackham (1934)]
    (Source)

Rackham notes that μακάριος ("blessed"/"happy") derives from μάκαρ, applied in Homer and Hesiod to the gods, and to humans admitted to the Islands of the Blessed. (Source (Greek)). Alternate translations:

For as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy.
[tr. Chase (1847)]

For a single day, or even a short period of happiness, no more makes a blessed and a happy man than one sunny day or one swallow makes a spring.
[tr. Williams (1869)]

For as one swallow or one day does not make a spring, so one day or a short time does not make a fortunate or happy man.
[tr. Welldon (1892), ch. 6]

For one swallow or one fine day does not make a spring, nor does one day or any small space of time make a blessed or happy man.
[tr. Peters (1893), 1.7.16]

For one swallow does not make a summer, nor does one day; and so too one day, or a short time, does not make a man blessed and happy.
[tr. Ross (1908)]

For one swallow does not make a spring, nor does one day. Nor, similarly, does one day or a short time make someone blessed and happy.
[tr. Reeve (1948)]

One swallow does not make a summer; neither does one fine day. And one day, or indeed any brief period of felicity, does not make a man entirely and perfectly happy.
[tr. Thomson (1953)]

For one swallow does not make a spring, nor does one day; and so too one day or a short time does not make a man blessed or happy.
[tr. Apostle (1975)]

One swallow does not make a summer; neither does one day. Similarly neither can one day, or a brief space of time, make a man blessed and happy.
[tr. Thomson/Tredennick (1976)]

For one swallow does not make a summer, nor one day. Neither does one day or a short time make someone blessed and happy.
[tr. Crisp (2000)]

For one swallow does not make a spring, nor does one day. And in this way, one day or a short time does not make someone blessed and happy either.
[tr. Bartlett/Collins (2011)]

For one swallow does not make a spring, nor does one day. Nor, similarly, does one day or a short time make someone blessed and happy.
[tr. Reeve (2014)]