"Eternal return" is the doctrine that every event in the universe, in all its details and in its whole cosmic context, will recur an infinite number of times in exactly the same way that it has already occurred an infinite number of times in the past. This doctrine must be distinguished from the belief in the general periodicity of nature, according to which the main features—but not the specific details—of human and cosmic history recur.

The Pre-Socratics

The periodicity of various phenomena is a fact of daily experience; the alternation of day and night, of lunar phases and of the seasons of the year, and the rhythm of breathing and heartbeats were known to primitive people. Even the idea that cosmic history repeats itself in its general features appeared in various forms in mythological thought. Among the pre-Socratics the idea was held by Anaximander...