The line 1.16 of Yoga Sutras refers to the category of “gunas”, thus in order to understand this line we need first to study out the meaning of this category, so let us proceed to this.
Normally each one who is somehow related to yoga even in its most “pop” variants has heard the terms that denote each of the three gunas – sattva, rajas and tamas. However the paradox here is that though using these terms in various applied aspects – starting from “Vedic” culinary art and up to Hatha-yoga – the majority of people don’t make any attempt to understand the definition: WHAT are the gunas in their general meaning. Moreover, they are not only pseudo-esoterics who are far from this understanding, but the experts in Indian culture and philosophy as well. It seems like everyone has so much got used to the category that they have all ceased “losing their sleep” over its core point. In most cases they introduce the three gunas through “pure Vishuddha”, i.e. by means of different metaphors. For instance, the Krishnaites prefer emotional metaphors: sattva is the loftiness and nobleness, rajas is the passion while tamas is the ignorance; the followers of Ayurveda are prone to describing it in physiological manner, for instance tamas is the sleepiness. Even the Indology experts use the metaphors, though their metaphors come close to notions of humanities. For instance, Max Mueller, the outstanding scientist, has correlated the three gunas with Hegel’s triad thesis-antithesis-synthesis.
Zimmer (Indian Philosophy, 295 pgs.with illust.) is using a less coherent system of metaphors, actually explaining each of the gunas separately. To his mind “sattva” that derives from sat – “to be” – is something good in its existence, something decent. Rajas in his understanding is something “impure”, something having “colors” (the periods), or, generally speaking, the dirt. The author reminds that rajas actually means the dust, the red dust that ten months a year circulates within the backing hot air of India and that in rainy season turns into a sticky heavy mud. The meaning of the word tamas does not incur any doubts – this is the “physical and spiritual darkness”. Obviously in terms of such “broken” explanation one cannot figure out what it is that turns these three categories into a unified philosophical object – the “three-guna”.
Dasgupta (The History of [Indian] Philosophy, I, 243-244) “insists upon the substance-nature of the gunas for he states that in Samkhya the quality does not exist without some material substance, and this is only the density of the substance that may vary, yet its presence is a must. The author understands Sattva to be the intelligence stuff, Rajas – the energy stuff, while Tamas is the mass stuff”. However in terms of modern physics we should understand that any substantiality is nothing more than a metaphor, thus we shall treat this as another metaphoric means of description.
Actually, just the way it happens rather often, in terms of a more profound study the issue has become even less clear than prior to such investigation. Nevertheless, let us try to figure it out.
As usual, in order to comprehend any complicated term we need to analyze its history and its usage in different contexts and situations.
Unfortunately, in such analysis we cannot be based upon the text of YS since this is the second category (after chitta – I hope the reader keeps this in mind) that the YS author does not give definition to, probably considering it to be obvious or common to his readership. That’s why we shall try to search for this category in other classical texts.
First and foremost we shall immediately find the category of guna in Mahabharata since it is numerously referred to in the sections of Mokshadharma, Anugita and – of course – the Bhagavad Gita. The whole 14th chapter of the last one is dedicated to this category, so that it even has the respective title – “The yoga of liberation from the three gunas”. Being the basic categories of Samkhya, the gunas can be found in Samkhya Karika and its classical commentaries. One can also find the system of description that very much resembles the three gunas – that is, the system of three doshas – in the Great Three classics of Ayurveda: Charaka Samhita, Sushruta Samhita and Ashtanga Hridayam Samhita. Thus we can see that the concept of three gunas penetrates into almost the whole of Indian spiritual heritage but for the Buddhism that according to Radhakrishnan had one fundamental difference from Samkhya, that is, the Buddhists did not use the categories of Prakriti and the concept of three gunas.
Here it is probably the Samkhya that comes as the most ancient darshana, being even older that the Buddhism  so we can suppose that it was Samkhya that has introduced the category of gunas into common usage; however it is still interesting to search for their prototypes in some even more ancient cultural layers.
It is the already mentioned V. L. Smirnov, the outstanding translator of Mahabharata [into Russian], who draws the most profound and thorough analysis of this issue in his conceptual article “Samkhya and Yoga”. I shall draw some excerpts here:
“Deussen believes that the earliest Upanishad that mentions the three gunas as they are is the “Shvetashvatara Upanishad”.
The author thinks that the earliest piece of literature heritage setting forth the theory of gunas is the “Shvetashvatara Upanishad” (I, 3; IV, 5; V, 7; VI, 3-4, 11) and draws attention to complete match of “Shvetashvatara” (IV, 5) with “Maharayania” (X, 5):
There is one unborn being (female), red, white, and black, uniform, but producing manifold offspring. There is one unborn being (male) who loves her and lies by her; there is another who leaves her, while she is eating what has to be eaten [transl. by Mueller – translator’s note].
Deussen refers himself to interpretation of this piece given by Shankara: the triple colour of the female being symbolizes the three gunas while the female being is the Prakriti. These very symbols Shankara sees in “Khandogya Upanishad” (VI, 4) that states that the world consists of three elements: the fire, the water and the food [or the earth in the English translation of Mueller – translator’s note]. All things consist of red (lohita), white (çukla) and black (krischnaj).
“Among Europeans it is Dalman, one of few researchers who had studied thoroughly the philosophical texts of “Mahabharata”, who is the strident zealot of differentiating between the early and the late Samkhya. The author asseverates that the “classical” Samkhya is secondary, derivative, while the epic Samkhya is the primary one. Dalman associates the early Samkhya with “Rigveda” and draws an interesting parallel: the “Rigveda” (VIII, 58, 2) tells:
One Sun gives birth to it all;
one dawn illuminates this (universe),
this One has given life to this All”.
In “Mahabharata” (XII, 350, 10) we find:
"The only Devourer of victims (Agni)
Draws in many places;
One wind in many places blows in the world.
And there is One purusha, without gunas, the manifold”.
In “Khandogya Upanishad” (VI, 3-4). “The III khanda says that “The only” – the Being according to the II khanda, wished to become many, to enter those three origins and beings: the fire (tejas), the water (apas) and the earth (anna). Then the Being said “Let me make each of these three tripartite”. The IV khanda tells that whatever originates from tejas is of red colour (like the live coals); that originating from water is of white colour; the one originating from earth is of black colour. Deussen considers this piece of “Khandogya Upanishad” to be the source of the gunas concept. The comparison of the Upanishad text with that of “Mokshadharma” speaks in favour of such opinion”.
By the way, we can find the analogous “trichromatism” of the “primary being” in Ayurveda texts. For instance, the Charaka Samhita in description of ojas (if translated verbatim from Sanskrit the word “ojas” means “vigour”, “strength”) gives the following (C.S.1.17.74-75.): “The substance abiding in one’s heart and coloured white, red or yellow is called Ojas. When the ojas leaves the body this body is subject to destruction, and so the man dies. The initial substance that is formed within the body of a developing living creature is the Ojas. It has the colour of drawn butter, tastes like honey and smells like fresh rice that has just been peeled. Like the bees gather honey from the tripped flowers and fruits, so all organs of the human body do accumulate Ojas for performing their functions”.
In this way, though probably by some stretching the point, we may consider the concept of gunas to come among the most ancient ones and to originate from Vedas. However we still lack the understanding of what these gunas are. So I will try to give my culturally and psychologically-based interpretation of this category.
I shall take a roundabout approach to this subject. It has been noticed that each culture has the description of its Universe based upon this or that number. There are the binary cultures, like the Chinese one that sees the world as a union of two elements – yin and yang. The binary cultures that are based upon figure 2 also included the Zoroastrian culture that was the first one to divide the universe into two elements fighting against each other: the good and kind one (Ahura Mazda) and the evil one (Angra Mainyu). The Greek culture enjoyed the figure 4: four primary elements, four cardinal directions, four seasons, psychological types etc. The Babylon culture worshipped the seven. We owe it the seven days of the week and the astrological septennaire. The late Buddhists used to draw it all to figure 6. We can continue drawing the instances, yet it is more important here that it was figure 3 that the Vedic culture used to pay respect and piety to. Just like every post-shamanistic cosmogony, the Universe of the ancient Aryans was divided into three parts (the three-loka): the lower world – Bhu, the middle one – Bhuvas, and the upper one – Svar. Such division was identical to the Scandinavian mythology triad: Hel – Midgard – Asgard, as well as to the pagan (or the neo-paganJ) triad of Nav’ - Yav’ – Prav’. We leave it up to the reader to search for denominations in other classical or neo-shamanistic systems. However what is important for us here is this very idea of the world triplicity in terms of the post-shamanistic mythology. I believe that initially the gunas proto-concept was related to this very triad. We can find verification of this opinion in some later sources that already bear some philosophical character and come as a sort of vestiges. For instance, the “Tattva Kaumudi” treatise tells that “Up above the sattva prevails, the tamas does so in the lower realms. In the middle the rajas is predominant”.
There is a number of other similar atavisms, for instance the correlation of sattva guna with some divine principle (that it superior in any case) and of tamas with some animal (inferior) one. This is confirmed by the opinion of Senart who believes the Vedic word “rajas” to stand for the light, the lucid layers of the Skies, that was opposed to tamas – the darkness of the Underworld.
Further on, in scope of the primary mystical worldview’ philosophization, the initial triad ceased to be associated with the elements of cosmogony hierarchy and became perceived in some more metaphoric manner acquiring the philosophical, ethical and even some medical sense. I think it was at this very stage that the word “guna” itself emerged, being literary translated as “the thread”, “the rope”, “the strand”. The primary principles were no longer subject to strict vertical hierarchization and were now seen as being intertwined in some complicated form, just like a simple rope that is spliced from the three strings in the “pigtail” manner, so the “gunas are circulating within the gunas”. Just like in other cultures, in terms of dialecticism development in philosophy there appears the idea about relative nature of primary elements, their intertransition-interconversion-interdependence. For instance, it is in this manner that the gunas concept is drawn in the “Anugita” (XIV, 39, 1 and further):
“The gunas cannot be explained altogether distinctly from one another. Rajas, Sattva, and Tamas are mixed up with one another. They are attached to one another, serve one another, they feed on one another. They all depend on one another, and likewise follow one another. They act, unperceived, by turns in the several places in several ways. Everything in the world is made of these three gunas. The creation of the gunas is eternal. As long as there is goodness so long, darkness exists. And, as long as goodness and darkness exist, so long the passion exists. They perform their journey together, in union, and moving about collectively”.
Thus the idea of the gunas hierarchic structure comes as a kind of vestige of some more archaic mythological layers.
Now that we know different groups of metaphors that describe sattva, rajas and tamas, let us find some common generalizing metaphor or some analogy that would take into consideration the hierarchic structure and relative nature of the gunas and would also co-opt all descriptions known as of today. However strange it may seem, yet the most appropriate option here is the “energetic” metaphor form the natural sciences.
That is, sattva can be correlated to potential energy of the system, rajas – to the kinetic one, while tamas is the lack of energy.
This metaphor complies with physiological descriptions and it is intuitively subject to hierarchization according to up to down axis. And indeed, the stone that hangs high above has the maximum potential energy (sattva); in terms of its falling down the potential energy is transformed into the kinetic one, while the stone that has fallen does not have any energy at all (tamas). Yet in relation to other objects that are under it (for instance, at some lower floors of the building) the stone still preserves the ability of falling down, i.e. its sattva is bigger. In scope of some other system that is moving relative to this stone it also possesses some kinetic energy, that’s why the qualities of sattva, rajas and tamas are not absolute yet they transfer one into another. The ancient Hindus were obviously not aware of the relativity principle but they had sufficiently dialectic mind and possessed a good number of observations from different spheres. For instance, the seed with its potency of making the new plant grow is sattvic in its nature, the plant in its full bloom is rajastic while the rotten fruit that has fallen from it is of tamas nature. But it is this very fruit that contains the new seed. The gunas are again “circulating within gunas”.
Another instance: the cloud filled with rainy moisture is sattvic, the rain is of rajas nature and the water on the ground is of tamas kind yet at the same time it is of sattvic nature since it contains the possibility of the new cloud to emerge and the new crop to be grown. The sex is rajastic, but it makes it possible for the new life to be conceived (sattva) or for one’s consciousness to “go on a trip” (tamas) and so on.
 Smirnov, “Samkhya and Yoga”.
 Here we can just recall that in the Buddhist tradition they believed the first teacher of Buddha to be Arada Kalama, the representative of Samkhya doctrine.
 Borrowed at the time of Babylonian captivity, this theory has migrated through Judaism into modern Abrahamic religions, including Christianity.
 Quoted as per the collection of works “The Moonlight of Samkhya” under the editorship of Shokhin V. K., pg.224