The swallow is a migratory bird, visiting Great Britain in April and leaving for warmer climes in September. As far as Great Britain is concerned, ‘spring’ is more accurate than ‘summer’. Aristotle, the Greek philosopher, wrote: ‘One swallow does not make spring, nor does one fine day’.
The proverb reminds us that winter is not necessarily over just because we have seen one swallow. By extension we are reminded also, that any single piece of evidence is not enough to prove anything. It may even be an exception.
An Albanian proverb on with the same meaning goes: ‘One flower does not make spring.’