Samkhya Karika 13

सत्त्वं लघु प्रकाशकमिष्टमुपष्टम्भकं चलं च रजः ।
गुरु वरणकमेव तमः प्रदीपवच्चार्थतो वृत्तिः ॥ १३ ॥

sattvaṁ laghu prakāśakamiṣṭamupaṣṭambhakaṁ calaṁ ca rajaḥ ।
guru varaṇakameva tamaḥ pradīpavaccārthato vṛttiḥ ॥ 13 ॥

sattvaṁ=sattva guna; laghu=light, buoyant; prakāśakam=illuminating; iṣṭam=desired, considered; upaṣṭambhakaṁ=exciting; calaṁ=restless; ca=and; rajaḥ=rajas guna; guru=heavy; varaṇakam=enveloping, obscuring; eva=indeed; tamaḥ=tamas guna; pradīpavat=like a lamp; ca=and; arthato=for the purpose; vṛttiḥ=function, operation

Sattva guna is light/buoyant and illuminating, the rajas guna is exciting and mobile, and tamas is heavy and enveloping. Like a lamp, they work together toward a specific end.

Sattva is light (in terms of weight) and illuminating. When sattva is dominant, one feels light in the body. Intellect becomes bright and can ascertain objects perceived by the sense organs with much more clarity. Rajas is mobile (fickle, unsteady etc.) and exciting. Both sattva and tamas are inactive by themselves. They need the driving force of rajas which can excite them into action so they can produce their own effects. When rajas is dominant, one can go into an overdrive and strive for more. It can also make one fickle-minded, unable to make proper decisions. When tamas is dominant, one can become lethargic, heavy, sleepy, indecisive and unable to act. The mind can become dull, unable to perceive objects clearly through the five senses.

Even though the three gunas seem to be mutually opposed to each other, they, however, work in a mutually cooperative manner to achieve the desired end result. The karika gives the example of a lamp wherein the wick, oil and the flame work together to produce light. Individually, or even in pairs, these three cannot produce the desired outcome, that of providing light.

The word “arthataH” in the second line has been interpreted differently by different authors. Its literal meaning is “for the purpose of”. Gaudapada takes the meaning to be “to attain the desire end result”. Mishra and a few others, on the other hand, extend the purpose to include the liberation of Purusha. You may recall that in the Yoga Sutra 2.18, Patanjali mentions that the purpose of Prakriti is to provide “bhoga” (life experience) and “apavarga” (liberation) for the Purusha. In this sense, the meaning is that the three gunas work cooperatively to attain the final goal of liberation for the Purusha.