The life of a human being encompasses all that he or she can experience in this lifetime. A life driven by the senses and desires runs aftersense objects: objects of desire which can be wealth, power, or hedonism. 

Somewhere between this drama of life, we take a pause as we become tired of the rat race and reflect fleetingly on what it is that we are running after? When this pause becomes more frequent, we turn our sense of perception from the outside to inside as we realise that each and every moment we are moving closer to the pyre and have very little time on earth to unearth the secret of our being. 
Our desires are never fulfilled by external objects, thus a sense of incompleteness engulfs us and we want to expand our horizon and gaze onto an unchartered pathway, the territory of spirituality. This is the ultimate fate of each human being on earth. The only difference is the time at which one feels this urge to know the limitless. Thus, the first line of Patanjali Yoga sutra starts with the sutra“Atha yoga anusashanam.” ‘Atha’ means now. It is a very powerful word. It is the present moment, the 'Now', that really matters. We have this moment, this 'Now', to be utilised fully. If only we were to look deeply, that the mystery of the universe would unfold within us. This can happen 'Now', i.e. atha, at this very moment, we only need the will. 

When one wants to move onto the spiritual path, the sense of perception needs to be refined. This is possible by purification of the heart through disciplines such as control of the senses, concentration, performing one’s rites or duties combined with devotion, being dispassionate, and being free of sin or deceit. The secret of moving from a limited entity bound by our physicality and mentality to boundless limitless formless pure consciousness is revealed only to those who have made necessary preparation, and have prepared the soil before sowing the seed. 

This knowledge of reality or the highest truthor Atman or Brahman, whatever one calls it, is eternally existent. It is obscured by the ignorance in thejiva. The aim ofsadhanais to remove this obstruction, to break this wall. 

We become eligible for knowledge of Atma (Brahma Vidya) only when we understand the relationship between Brahma and humanity in the cosmic cycle of creation and destruction. ‘Brahma’ means the vast, infinite principle. The element of sound (akasa) emanated from this infinite expanse of Brahma. From sound emerged air (vayu), fire (tejas) from air, wind from fire, earth (prithvi) from wind, oceans from earth, food from oceans, and finally, humans from food. Ponder this sequential cycle and you will arrive at the truth that humanity has emerged from the infinite Brahma. 

The purpose of enquiry: 
Now the question that arises in our minds is that why should I learn about the nature of reality, why should I inquire? How would it help me in my day-to-day life? The answer given by Vedanta is when we realise the truth, our fundamental outlook on how we look at life changes, and so we can have a better handle on our life. We have two ways of enjoying a theatrical show. The actors who take part in it, and the spectators, both enjoy the show. The actors identify themselves with the characters and take the show as real. Therefore, they cannot enjoy the show in reality. But the spectators know the unreality of the show and are detached from it, and so they really enjoy it. So, we have two ways to look at life. When we are spectators or witness to this drama of life, we will really enjoy it. In the language of Shankara, the knowledge of reality cuts through our ignorance and dehypnotises our mind so that it destroys our hankering for objects which are unreal. The elimination of ego is the basic requirement for acquiring any knowledge. When a glass is empty you can fill it. If we pour water in glass which is full, it will only overflow. So, the first step is to make our conditioned mind empty of all preconception and eliminate our ego. The whole of life is thus an ongoing process or, yoga, or discipline or path to realise the truth. The goal is as important as the way, the path. TheSadhana Chatusthay for this is discrimination, renunciation, self-control and an irrepressible urge for the realisation of truth. 

Thus, our sense of perception is the doorway to this mystery of our being. If we closely observe our lives, we find that we move seamlessly between three states of awakening, dream, and deep sleep on a daily basis. The well-known method of Vedanta to arrive at reality is what is known as vichara or contemplation and discrimination. In Mandukya Upanishad, we find the problem of handling the ultimate reality straightforward. Thus, it goes on to illustrate the three states of our existence and also posits a fourth state and its significance.The experiencer of the three states, also known as ‘Viswa’, ‘Taijasa’, and ‘Prajna’, or, Waking (Wakefulness), Dream and Deep Sleep is only one. The fourth, or the ‘Turiya’ is the Atman or Brahman. 

Now let us explore in detail the three states of our being and inquire about the fourth state in the light of the Mandukya Upanishad with Goudapada’s Karika and commentary of Shankara. Goudapada lays emphasis on the fact that it is impossible to reach the highest truth until and unless the totality of human experience or knowledge can be taken into consideration. The Upanishads show us that unless the three states of Waking, Dream and Deep Sleep are coordinated, there cannot be adequate data for the inquiry of the ultimate truth. According to Goudapadacharya and Shankaracharya, philosophy is an interpretation of the totality of human experience, or of the whole of life from the standpoint of truth. It does not only relate to the waking state.Goudapadacharya was the Guru of Govindacharya who was the Guru of Shankaracharya. In that sense, Goudapadacharya was the great-grand-Guru of Shankaracharya. 

Brahman is Aum : 
The phenomena of the world consists of ideas or the mental states. The ideas can be expressed as words. The utterance of the word AUM is the clue to the pronunciation of all the words used by human beings. It is the substratum of all the sounds. As Shabda Brahman, Brahman is also the substratum of all objects, animate or inanimate and is all pervading.Not only this, it is the substratum of all phenomena. The sound signifying the phenomena is non-different from the phenomena. Hence, Brahman is AUM. The AUM which represents the phenomena of Brahman has three mantras. A (The waking state), U (The dream state) and M (The deep sleep state). It has one Amatra, which is the silence after AUM. This is the fourth, The Turiya. This Turiya is Brahman. 

In Kathopanishad, it is mentioned that when AUM is uttered with concentration, there arises the consciousness of Brahman in the mind. Through the meditation on AUM, one can realise both thepara(attributeless) Brahman andapara(name and forms) Brahman. One who seeks to realise the self with one point concentration on AUM feels that the gross universe (A) is absorbed into the subtle (U) and (U) then into the causal (M), and finally the universe, dependent on the causal relation is withdrawn into the transcendental, which is known asAmatra,and which cannot be designated by any letter or sound. It is this stillness which is ‘the fourth’, theTuriya or The Brahman. 

The Upanishads elaborate on the principle of Brahman through three names:Viraat, Hiranyagarbha, andAvyaakruta or Iswara. These three forms relate to Gross (Sthulam), Subtle(Sukshmam), and Causal(Kaaranam)and to the three states ofWaking, Dream, and Deep Sleep. The transcendental Brahman or the Turiya i.e. The Fourth is beyond all causal relations and is the ultimate substratum of all appearances i.e. Virat, Hiranyagarbha and Iswara. 

In Agama Prakarana, the first chapter of Mandukya Upanishad, it is said, “All this is verily Brahman. This Atman is Brahman. This Atman has four quarters or fourpadas.” These fourpadasare not like the legs of cows which are unrelated to each other. These fourpadasare the quarters of a coin orKarshapana.The quarter is merged in the half coin. The half is merged into three fourths and the three-fourths is merged in the full. So the Viswa or Waking State is merged in Taijasa, The Dream State and Taijasa are merged in Prajna or Deep Sleep State. Finally, Prajna is merged in Turiya, The Fourth. So, the Fourth or Turiya is realized by merging the three states in it.This fourth state or Turiya is the object of enquiry. 

The four padas or quarters : 
1. The first quarter is the Viswa, the Waking State:It is said in the Mandukya Upanishad, “The first pada is Vaiswanara, whose sphere of activity is the waking state, who is conscious of external objects, who has seven limbs and nineteen mouths, and whose experience consists of gross objects.” 
His sphere of activity is theJagritsthana or Waking State.Because of ignorance oravidya,consciousness appears as related to outward objects other than himself. So he isbahishprajna.He is saptanga i.e., having seven limbs in his body. Seven limbs: The word ‘limbs’ is used here to denote parts of the body. The seven limbs are the Head, the Eyes, the Mouth, the Breath, the Middle Part of the Body, the Kidney, and the Feet. They have their counterparts in the universe viz, the Heavens, the Sun, Fire, Air, Akasa (space), Water, and Earth. He has nineteen mouths, which means, five organs of perceptions(Buddhindriyas),five organs of actions(Karmendriyas),five aspects of vital breath (Prana, etc),the mind(Manas), the intellect(Buddhi),egoity(ahankara),mind-stuff (Chitta). These are the instruments by which Vaiswanara experiences objects.He is non-different from the totality of gross bodies orVirat. He is the first quarter, as the subsequent quarters are realized through him.He is calledVaiswanara, i.e. All Beings since He encompasses all beings by virtue of His being non-different (in reality) from the self, i.e.Virat comprising all the gross bodies. 

The Parallelism Between Microcosmic And Macrocosmic : 
 
He exists in everyone but is undetected. He performs all actions but behaves as if He does not. He experiences everything but does not reveal it. Therefore, Viraat is the principle that manifests as the external, gross, visible world.The universe may be seen from two standpoints: TheMicrocosmic and The Macrocosmic. TheMicrocosmic (subjective) entity(Adhyatma) is endowed with four quarters, namely,Vaisvanara (or Visva), Taijasa, Prajna, and Turiya. Likewise, themacrocosmic (objective) universe, comprising the sphere of the sun, the moon, the stars, etc., has four quarters.The first three are known asVirat(the totality of gross physical bodies),Hiranyagarbha(the totality of subtle bodies),and Isvara orAvyakrita, the unmanifested (the totality of causal bodies). The attributelessBrahman,likeTuriya, is the fourth.  

It is transcendental, beyond all causal relations, and is the unrelated substratum of all appearances. A parallelism runs through the subjective and the objective. The macrocosm is superimposed upon Brahman, and the microcosm upon Atman (Self), through Avidya (ignorance). Both are illusory appearances. On account of the non-difference between the subjective and the objective, the limbs of Vaisvanara are described in terms of the objective universe. The purpose is to show the illusory nature of the entire phenomenal world and establish the non-duality of Atman (Self) and Brahman (Supreme Reality). 

2. The second quarter is Taijasa or The Dream State:“It is the second quarter and its sphere of activity is the dream state whose consciousness is internal, who is possessed of seven limbs and nineteen mouths, and also enjoys subtle objects.” 
Thus, the sphere of activity isSwapnasthanah.The wakingconsciousness, as it is associated with many means and being conscious of objects as if external, are nothing but states of mind, leaves in the mind corresponding impressions.Under the illusion of ignorance, desire, and past action, the mind thus possessed of the impressions like a piece of painted canvas makes its appearance in The Dream State just as in the waking state but without any external means. The mind is aware of internal objects orAntah(internal)Prajna(awareness).Here the enjoyment is subtle. He is calledTaijasaor luminous since he becomes the witness of the cognition that is bereft of objects and appears only as a luminous thing. The object of experience is consciousness consisting ofVasanas, i.e. impressions of past experiences. 

The second form of Brahman is Hiranyagarbha: the basis, the source of all wisdom. All knowledge — worldly, ethical, dharmic, spiritual, scientific — has emanated from Hiranyagarbha. Therefore, He is also called the Sun of Knowledge(Jnana Bhaskara). When the sun rises, He appears golden (Hiranya) and colours the world with a golden hue. 
 
Hiranyagarbhais a sanskrit term that translates to ‘golden embryo’, ‘golden womb’ or ’golden egg’. It is derived from the root words‘hiranya’, meaning golden or, wealth, and‘garbha’, meaning womb, germ/seed or essence. Creation emerged from Hiranyagarbha, which is oval in shape like an egg. The mouth was the first to emerge from this shape. From the mouth, sound. Then, the nose, through which air began flowing. Eyes came next, with fire emanating through them. Ears arrived next. Therefore,Hiranyagarbhais the origin of the human form. Hiranyagarbha, like Viraat, has two other names:Sutraatmaka and Praana. Just as a thread (sutra) passes through a necklace of gems, Sutraatmaka is the principle that underlies all beings and brings bliss to them. This unifying thread-like principle is also calledBrahma Sutra. 

Hiranyagarbha assumes a subtle (sukshmam) form during the dream state — the form of the Atma. This means that Hiranyagarbha is one who is awake during the dream state. Viraat creates everything in the waking state. Hiranyagarbha creates everything in the dream state by mere willing. Every object is created by will alone. Whatever is seen in dreams is created by Hiranyagarbha. 
 
The reflection of the body(Deham)is the external world (Desam).“Outside is a reflection of the inner Being.” 

3. The third quarter is the Prajna or The Deep Sleep State:“That state is Deep Sleep where the asleep individual does not desire anything and hence does not see any dream. The third state is calledPrajnai.e. where all experiences become undifferentiated, which is a mass of mere consciousness, which abounds in bliss, where one is surely an enjoyer of bliss, andwhois the doorway to the experience of the two other states of waking and dream.” 
The sphere of the Deep Sleep state isSusuptasthana.He is said to beeki bhutah, i.e. undifferentiated. Conscious experiences that are but vibrations of the mind in the waking and dream states, become as they were. This state is calledPrajnanaghanah, a mass of consciousness, since it is characterised by the absence of discrimination. The word ‘eva’ denotes verily i.e. the absence of any other thing except consciousness. He isAnandamayah,full of joy, his abundance of joy being caused by the absence of misery involved in the effort of the mind vibrating as the objects and their experiencer. But he is not bliss itself as the joy is not absolute and the bliss is not infinite. He isAnandabhuk,the experiencer of joy. What is common to all the three states is the absence of the knowledge of reality. He isCetomukhah, since he is the doorway to the consciousness of the experiences in the dream and waking states. 
The third form of Brahman isAvyaakruta. He is absolutely formless. He exists in the causal body and enjoys the state of deep sleep. He has no limbs but does all actions. He travels to distant places. He has no eyes but sees everything. He has no ears but listens to everything. He performs the act in Creation, but possesses no form. He also has two more names: 
 
Antaraatma and Iswara. Antaratmais the inner voice as all inspiration, urge and every motive comes from thisantaratma. Iswara is the embodiment of all forms of prosperity (Sakala Aisarwa Swarupa). 
 
Jagrat, Swapna and Sushuptiare the three states where the perceiver experiences the three states. The common term used for them isSuptawhich denotes the absence of knowledge of reality. ‘Sushupti’is designated as the state of causal unity of waking and dream state from the stand point of a waking man. But this is also a ‘vritti’ in the mind of a waking man to find the cause of waking and dream state. The perceiver in the ‘jagrat’ and ‘swapna’ states, who always experiences subject-object relationship, finds its absence in Sushupti. 
 
Atman The Witness : 
 
Goudapada says,“It is only one alone who is thus known in the three states.”It denotes theAtman(the witness) is distinct from these three states (i.e. the witnessed). As a powerful fish swims from one bank of the river to the other unimpeded by the currents of the river, so alsoAtmanmoves in the three states totally unaffected by them. No experiences of the three states affect the pureAtman. 
 
4. The Fourth state TURIYA: It is sought to be indicated by the negation of all attributes- Brahman appears as the world without forfeiting its essential nature just like the classic Advaitic example of a rope that appears to be a snake. The fourth is not the fourth state or condition in whichAtmanhas to be viewed.Turiya which is indicated here as the “fourth” and which actually means the fourth step, comes into consideration only when all the other three states have been considered. Atmanitself does not admit of any conditions or states. Waking, dream and deep sleep are its three states or quarters, butTuriya,the fourth is actually present in all these three states. 
 
“Turiyais not that which is conscious of the internal (subjective) world nor it is conscious of the external (objective) world. Neither that which is conscious of both nor a mass of consciousness. Neither conscious nor unconscious. It is unseen (by any sense organ), incomprehensible (by the mind), beyond the grasp (of the organs of action), un-inferrable, indescribable, unthinkable, essentially of the nature of the consciousness, constituting the self alone, in which all phenomena cease, which is unchanging, peaceful, auspicious, all bliss and the non-dual. That is what is known as the “Fourth”(Turiya). This is the Atman and it has to be realised.” 
Thus, ultimately, it is said that Duality cannot exist, the highest truth (non- duality) is realised. It is shown that the meaning of theVedic statement, "That thou art” points to the relationless Atman (Turiya), which is like the rope, different from the snake. 
Goudapadacharya, according to the scriptures, prescribesAsparsa Yogaas the means to realise this Turiya. Theterm Asparsa Yoga means ‘yoga of non-contact’. Here, ‘yoga’ is not used in the sense of union, but as discipline or path. The word asparsa denotes freedom from relationships and refers to the non-dual Brahman alone. So, theAsparsa Yogais the path or discipline which leads to the freedom from relationships or non-dual Brahman. This alone is beneficial to all beings and can bring joy to all. 

Courtesy: http://www.pragyata.com/mag/significance-of-knowing-the-fourth-740