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 VEDA 
jñānena tu tad ajñānam yeṣāṃ nāśitam ātmanaḥ | teṣām ādityavaj jñānaṃ prakāśayati tat param
“As the sun dispels darkness and illuminates everything, so divine knowledge destroys ignorance and reveals the transcendental Absolute Truth.” — Bhagavad-Gītā 5.16    

Triguna – sattva, rajas und tamas

Of the three qualities (triguṇa) or modes of material nature (prakṛti) – sattva (purity, virtue, goodness), rajas (passion) and tamas (inertia, darkness, ignorance) – rajas and tamas are described in the Ayurvedic classical text Caraka-Saṃhitā (Sūtrasthāna 1. 57) as psychic doṣas (faults, blemishes). Everything in this world is subject to the influence of these three guṇas. They are primordial elements from which all manifestations of the material world arise and they pervade everything. The living beings in this world almost all think and act under the mixed influence of the guṇas, with one mode usually predominating.

People who are mainly conditioned by the mode of goodness feel happy and contented and develop knowledge. Other qualities of sattva-guṇa are liberality, compassion, renunciation, simplicity, humility, freedom from attachment, self-control, fearlessness, faith in the revealed Vedic scriptures, forgiveness, courage, non-violence, equanimity, gentleness, kindness, purity. People who are mainly conditioned by the appearance of purity are full of happiness and contentment and develop knowledge.

People who are mainly conditioned by the mode of passion are full of desires and cravings and very active in fulfilling them or satisfying them. In the Mahābhārata it is said:

“Beauty, work, joy and sorrow, heat and cold, power, war, peace, arguments, discontent, pride, strife, ill-will, buying and selling, cruelty, pointing out the faults of others; thoughts directed only to worldly affairs; worry, blasphemy, hesitation and doubt, boasting, bravery, obedience, prudence, heedlessness, diplomacy, possessiveness, sorrow, vows, rites, public welfare work, giving instructions, performing sacrifices for the sake of material gain, giving gifts in expectation of advantage, deceit, respect and disrespect, stealing, indulgence, attachment, gambling, dancing, making music, etc. – all these qualities belong to the material mode of passion. . . .”

“. . . . Illusion, ignorance, indecision, too much sleep, arrogance, absence of confidence, vicious behaviour, fear, greed, craving for criticism, lack of discernment, hostility towards all living beings, malice, foolish reasoning, sinfulness, folly, callousness, speaking ill of others, blaming the brāhmanas and the devas, vanity, anger, eating more than is necessary, evil slandering – all these qualities belong to the material mode of ignorance.”

Sattva, rajas and tamas bind the living beings to material nature. He who cultivates the material mode of virtue in his life may go to heavenly planets after death, he who leaves his body in rajo-guṇa may take birth again as a human being on earth, and he who leaves his body in tamo-guṇa may be reborn as an animal or a plant or on hellish planets.

In the Bhagavad-gītā, the three guṇas are analysed in terms of faith, happiness, sacrifice, donations etc. The predominance of one of the three guṇas depends, among other things, on the association one maintains and the food a person eats. Grains, pulses, milk and milk products, nuts, vegetables, fruits, sugarcane products etc. promote sattva-guṇa in man if they are prepared and consumed in the right way. Bhagavad-gītā 17.8-9 states:

“Food that is appreciated by people in the material mode of goodness prolongs life, purifies existence and gives strength, health, happiness and contentment. Such foods are succulent, fatty (ghee, butter and vegetable oils), wholesome and gladden the heart.

Foods that are too spicy, too hot, too salty, too acidic, biting, burning and too dry/rough promote rajas and are appreciated by people who are in this mode. Such food causes pain, suffering, and disease.”

Food in the mode of ignorance includes fermented food; food that is tasteless and stale; food consisting of leftovers and untouchable things (e.g. bones, meat and other substances from dead animals). Eggs, mushrooms, alcoholic drinks and other intoxicants, tobacco, narcotics, etc. are substances that promote tamo-guṇa in humans and are preferred by such people.

Diet and other activities in the mode of passion and ignorance cause morbid impairment of vāta, pitta, kapha and consequently disease, pain and suffering arise.

To think that each of the three physical doṣas is absolutely related to a mental doṣa – e.g. pitta to rajas or kapha to tamas and vata to sattva – is certainly a mistaken idea. Foods and substances that over-stimulate kapha, vāta and pitta can promote tamas and rajas – this interaction exists, but one cannot absolutely attribute a particular physical doṣa to a particular mental doṣa.

In Vedic culture, of the four classes of society in general, brāhmanas (doctors, priests and scholars) acted mainly under the influence of sattva-guṇa, kṣatriyas (kings, warriors and administrators) under the influence of rajo-guṇa, vaiśyas (farmers and traders) under the influence of rajas and tamas and śudras (labourers, craftsmen, artists) under the influence of tamas.

In the kali-yuga, the present age, almost everyone acts under the influence of rajas and tamas. The influence of sattva-guṇa declines and the influence of tamas becomes stronger as this age progresses. All three guṇas are present in each age, but not to the same extent. In the satya-yuga, sattva is predominant – people are happy and contented, self-controlled, renounced, strong, long-lived, etc. In the treta-yuga, rajas gradually gains influence, in the dvāpara-yuga it becomes stronger and tamas gradually comes into play, which in the kali-yuga becomes the dominant mental doṣa, with all the symptoms of madness and illusion. Diseases increasingly manifest under the influence of rajas and tamas. Today's medical knowledge and their approach to disease is also a symptom of rajas and tamas. Instead of eliminating the roots of disease – acting under the influence of rajas and tamas – a vast medical industry is set in motion that is just as pathological, just as dominated by rajas and tamas, as that which it seeks to eliminate.

Those who strive for happiness and health must overcome the influence of rajas and tamas by keeping away from anything that stimulates these two psychic doṣas. And one who aspires for liberation from the bondage of material nature must perform transcendental activities in connection with the Supreme (e.g., study of the Bhagavad-gītā and other Vedic scriptures, japa, śravanam kīrtanam viṣṇu smaranam), overcoming all three – tamas, rajas and sattva. The transcendental level is called śuddha sattva. It is stated in the Śrīmad-Bhāgavatam (10.28.15):

“. . . .Great sages and saints who have overcome the influence of the three modes of material nature are able to see the spiritual world directly.”

It should be noted that times of day and seasons are also subject to the influence of the guṇas. The early morning hours – especially brahma-muhurta, the hour before sunrise – are sattva, from noon onwards the influence of rajas increases and from evening onwards the influence of tamas. Of course, the seasons are also subject to the influence of sattva, rajas and tamas, as are the four ages satya-, treta-, dvāpara- and kali-yuga. A person anchored at the śuddha sattva level is not subject to this influence.

Note: There is also a short video on the knowledge of the three gunas as part of a textbook on the Ayurveda substance doctrine.