The Purāṇas portray time as fundamentally cyclical rather than linear, unfolding through recurring world ages known as yugas. These four yugas—Satya (or Kṛta), Tretā, Dvāpara, and Kali—form a complete cycle called a mahāyuga, which spans 4,320,000 human years. In this vision, the universe is not moving toward a single final endpoint; instead, creation, preservation, and dissolution repeat in vast rhythms, with each cycle witnessing a gradual decline of righteousness and spiritual clarity, followed by renewal.

Within a mahāyuga, Satya Yuga is described as the age of truth and complete dharma, when virtue stands firm on all four metaphorical legs. Human beings in this age are depicted as long-lived, naturally virtuous, and spiritually advanced. In Tretā Yuga, dharma diminishes by one quarter, standing on three legs, and ritual sacrifices and formal religious practices become prominent as direct spiritual insight begins to wane. Dvāpara Yuga sees dharma reduced by half, standing on two legs, accompanied by increasing conflict, disease, and division in knowledge and practice. Kali Yuga, the present age, is marked by a three-quarters decline in righteousness, with dharma precariously supported on a single leg, and characterized by moral degradation, spiritual ignorance, and shortened lifespans.

The Purāṇic cosmology embeds these four yugas into progressively larger temporal structures. One mahāyuga, composed of the four yugas in sequence, is multiplied a thousandfold to constitute a kalpa, described as a “day of Brahmā.” After such a day, there follows a night of equal duration, a period of dissolution (pralaya) during which the manifested worlds are withdrawn. This alternation of cosmic day and night continues for 360 such days to form a year of Brahmā, and Brahmā’s full lifespan extends for 100 of these years, after which a far greater dissolution occurs and the entire cycle of creation is said to begin anew.

From a spiritual standpoint, this doctrine of cyclical time serves several intertwined purposes. It relativizes all worldly conditions, reminding the seeker that even the longest-lived beings and most stable cosmic orders are subject to rise and fall. It also provides a moral map: as the ages progress and dharma declines, the challenges to spiritual life increase, yet the Purāṇas simultaneously affirm that divine guidance continues through the appearance of avatāras who restore and protect righteousness in each yuga. The present Kali Yuga, though marked by conflict and confusion, is thus not merely an age of despair, but a context in which earnest turning toward dharma and the divine becomes all the more urgent and meaningful.