Tamas (Sanskrit: तमस् tamas "darkness") is one of the three Gunas (tendencies, qualities, attributes), a philosophical and psychological concept developed by the Samkhya school of Hindu philosophy. The other two qualities are rajas (passion and activity) and sattva (purity, goodness). Tamas is the quality of inertia, inactivity, dullness, or lethargy.
In Samkhya philosophy, a guṇa is one of three "tendencies, qualities": sattva, rajas and tamas. This category of qualities have been widely adopted by various schools of Hinduism for categorizing behavior and natural phenomena. The three qualities are:
- Sattva is the quality of balance, harmony, goodness, purity, universalizing, holistic, positive, peaceful, virtuous.
- Rajas is the quality of passion, activity, being driven, moving, dynamic.
- Tamas is the quality of dullness or inactivity, apathy, inertia or lethargy.
Action that is virtuous, thought through, free from attachment, and without craving for results is considered Sattvic; Action that is driven purely by craving for pleasure, selfishness and much effort is Rajasic; Action that is undertaken because of delusion, disregarding consequences, without considering loss or injury to others or self, is called Tamasic.
— Bhagavad Gita, Chapter 18, verses 23–25 
In Indian philosophy, these qualities are not considered as present in either-or fashion. Rather, everyone and everything has all three, only in different proportions and in different contexts. The living being or substance is viewed as the net result of the joint effect of these three qualities.
According to the Samkya school, no one and nothing is either purely Sattvic, Rajasic or Tamasic. One's nature and behavior is a complex interplay of all of these, with each guna in varying degrees. In some, the conduct is Rajasic with significant influence of Sattvic guna, in some it is Rajasic with significant influence of Tamasic guna, and so on.
The Sikh scripture refers to Tamas in its verses:
- "The Fourteenth Day: One who enters into the fourth state, overcomes time, and the three qualities of raajas, taamas, and satva"(SGGS )
- "Those who embody the energies of sattva-white light, raajas-red passion, and taamas-black darkness, abide in the Fear of God, along with the many created forms." (SGGS )
- "Your Power is diffused through the three gunas: raajas, taamas and satva" (SGGS )
- "Raajas, the quality of energy and activity; Taamas, the quality of darkness and inertia; and Satvas, the quality of purity and light, are all called the creations of Maya, Your illusion. That man who realizes the fourth state - he alone obtains the supreme state" (SGGS )
- James G. Lochtefeld, Guna, in The Illustrated Encyclopedia of Hinduism: A-M, Vol. 1, Rosen Publishing, ISBN 9780823931798, page 265
- Peter Schrijver (1995). Studies in British Celtic Historical Phonology. Rodopi. p. 221. ISBN 90-5183-820-4.
- Alter, Joseph S., Yoga in modern India, 2004 Princeton University Press, p 55
- Feuerstein, Georg The Shambhala Encyclopedia of Yoga, Shambhala Publications, 1997
- Alban Widgery (1930), The principles of Hindu Ethics, International Journal of Ethics, Vol. 40, No. 2, pages 234-237
- Whicher, Ian The Integrity of the Yoga Darśana, 1998 SUNY Press, 110