Guṇa (Sanskrit: गुण) means 'string' or 'a single thread or strand of a cord or twine'. In more abstract uses, it may mean 'a subdivision, species, kind, quality', or an operational principle or tendency.
In Samkhya philosophy, there are three major guṇas that serve as the fundamental operating principles or 'tendencies' of prakṛti (universal nature) which are called: sattva guṇa, rajas guṇa, and tamas guṇa. The three primary gunas are generally accepted to be associated with creation (sattva), preservation (rajas), and destruction (tamas) (see also Aum and Trimurti). The entire creation and its process of evolution is carried out by these three major gunas.
Classical elements 
The term guṇa in Classical Sanskrit literature in general (e.g. Mahabharata, the Bhagavata Purana, etc.) is the term for the five elements (mahabhutas), as well as the five senses, and five associated body parts:
- Akasha (space), associated with the guṇa śábda ("sound") and with the ear.
- Vayu (air), associated with the guṇa sparśa ("feeling") and with the skin.
- Tejas or Agni (fire), associated with the guṇa rūpa ("appearance", and thus color and tangibility) and with the eye.
- Apas or Jalam (water), associated with the guṇa rasa ("taste", and thus also flavor and tangibility, as well as shape) and with the tongue.
- Prithivi (earth), associated with all the preceding guṇas as well as the guṇa gandha ("smell") and with the nose.
Bhagavad Gita 
The Triguna appear prominently in the discourse of Krishna to Arjuna upon the battlefield of Kurukshetra that is the backdrop for the Bhagavad Gita. All three gunas are held to delude the World:
- त्रिभिर्गुणमयैर्भावैरेभिः सर्वमिदं जगत्।
- मोहितं नाभिजानाति मामेभ्यः परमव्ययम्॥ ७.१३॥
- tribhirguṇamayairbhāvairebhiḥ sarvamidaṁ jagat |
- mohitaṁ nābhijānāti māmebhyaḥ paramavyayam || 7.13||
- The World deluded by these Three Gunas does not know Me:
- Who is beyond these Gunas and imperishable. (7.13)
In Samkhya philosophy 
In Samkhya philosophy, a guṇa is one of three "tendencies": tamas, sattva, and rajas. These categories have become a common means of categorizing behavior and natural phenomena in Hindu philosophy, and also in Ayurvedic medicine, as a system to assess conditions and diets. For this reason Triguna and tridosha are considered to be related in the traditions of Ayurveda. Guṇa is the tendency, not action itself. For instance, sattva guṇa is the tendency towards purity but is not purity itself. Similarly rajas guṇa is that force which tends to create action but is not action itself. Each of the three gunas is ever present simultaneously in every particle of creation but the variations in equilibrium manifest all the variety in creation including matter, mind, body and spirit.
All creation is made up by a balance composed of all three forces. For creation to progress, each new stage "needs a force to maintain it and another force to develop it into a new stage. The force that develops the process in a new stage is rajo guna, while tamo guna is that which checks or retards the process in order to maintain the state already produced, so that it may form the basis for the next stage".
- Sattva (originally "being, existence, entity") has been translated to mean balance, order, or purity. Indologist Georg Feuerstein translates sattva as "lucidity".
- Rajas (originally "atmosphere, air, firmament") is also translated to mean change, movement or dynamism. (Rajas is etymologically unrelated to the word raja.)
- Tamas (originally "darkness", "obscurity") has been translated to mean "too inactive" or "inertia", negative, lethargic, dull, or slow. Usually it is associated with darkness, delusion, or ignorance. A tamas quality also can refer to anything destructive or entropic. In his Translation and Commentary on the Bhagavad-Gita, Maharishi Mahesh Yogi explains "The nature of tamo guna is to check or retard, though it should not be thought that if the movement is upward tamo guna is absent".
In Nyaya philosophy 
In Nyaya philosophy, 24 guṇas are enumerated as properties or characteristics of all created things, including śábda, sparśa, rūpa, rasa, and gandha.
- rūpa: appearance (shape and color).
- rasa: taste.
- gandha: smell.
- sparśa: feeling (touch).
- sāṃkhya: amount.
- parimāṇa: dimension.
- pṛthaktva: distinctness.
- saṃyoga: conjunction.
- vibhāga: disjunction.
- paratva: remoteness.
- aparatva: proximity.
- gurutva: gravity.
- dravatva: fluidity.
- sneha: viscidity.
- śábda: sound.
- buddhi/jñāna: enlightenment/knowing.
- sukha: pleasure.
- duḥkha: pain.
- icchā: desire.
- dveṣa: aversion.
- prayatna: effort.
- dharma: merit or virtue.
- adharma: demerit.
- saṃskāra: the self-reproductive quality;
In grammar 
In the Sanskrit grammatical tradition (Vyakarana), guṇa is a technical term corresponding to what is now termed the full grade in Indo-European ablaut. That is, it refers to a set of normal-length vowels that are less reduced than the basic set (in modern terms, the zero grade), but more reduced than the vṛddhi vowels (in modern terms, the lengthened grade). As an example, ṛ, i, u are basic (zero-grade) vowels, with corresponding guṇa (full-grade) vowels ar, e, o and vṛddhi (lengthened-grade) vowels ār, ai, au. (This is more understandable once it is realized that, at an earlier stage of development, Sanskrit e and o were ai and au, and Sanskrit ai and au were āi and āu.) This classification was developed by Pāṇini in his Ashtadhyayi.
In medicine 
In the terminology of Ayurveda (traditional medicine), guṇa can refer to one of twenty fundamental properties which any substance can exhibit, arranged in ten pairs of antonyms, viz. heavy/light, cold/hot, unctuous/dry, dull/sharp, stable/mobile, soft/hard, non-slimy/slimy, smooth/coarse, minute/gross, viscious/liquid.
See also 
- http://books.google.com/books?id=pSLU7SxSqHwC&pg=PA74&dq=rajas+guna&ei=ZTnrScPHDJbcMZ27qeQE#PPA76,M1 Hindu Philosophy, Theos Bernard, Motilal Banarsidass Publ: 1999, ISBN 978-81-208-1373-1, pp. 74–76.
- Autobiography Of A Yogi, Paramahansa Yogananda, Self Realization Fellowship, 1973, p.22
- Maharishi Mahesh Yogi on the Bhagavad-Gita, a New Translation and Commentary, Chapter 1-6. Penguin Books, 1969, p 128 (v 45)
- Maharishi Mahesh Yogi on the Bhagavad-Gita, a New Translation and Commentary, Chapter 1-6. Penguin Books, 1969, p 269 v.13
- Alter, Joseph S., Yoga in modern India, 2004 Princeton University Press, p 55
- Feuerstein, Georg The Shambhala Encyclopedia of Yoga, Shambhala Publications, 1997
- Whicher, Ian The Integrity of the Yoga Darśana, 1998 SUNY Press, 110
- Macdonald, Arthur Anthony (1927), A Sanskrit Grammar for Students p. 11. Oxford: Oxford University Press ISBN 0-19-815466-6
- * Chopra, Ananda S. (2003). "Āyurveda". In Selin, Helaine. Medicine Across Cultures: History and Practice of Medicine in Non-Western Cultures. Norwell, MA: Kluwer Academic Publishers. pp. 75–83. ISBN 1-4020-1166-0. p. 76, citing Sushrutasamhita 25.36.