A Brief History of Yoga
1. Vedic Age (4500 - 2500B.C.E.)
A. Vedas-Sacred scriptures of Brahmanism. 4 Books Rig, Sama, Yajur, Atharva.
B. Rig Veda- Oldest of the Texts. First mention of the word "yoga" referring to "yoking" or "discipline". Offers no method of practice.
C. Vratya Kanda- 15th book of Atharva Veda. First mention of pranayama

2. Pre-Classical Age (2500 - 100B.C.E.)
A. Upanishad- First mention of concepts of Karma, Cycles of birth and death, The ultimate reality (Brahman), the transcendental self (Atman), and the relationship between the two.
B. Brahman- Believed that everything exists within the consciousness (Brahman) nothing exists outside. Everything was a manifestation of the Divine (Non Dualistitc)
C. Karma Yoga- The path of action or ritual.
Jnana Yoga-The path of knowledge or intense study of the scriptures. Both paths were developed to lead the student to liberation from suffering and eventual enlightenment.
D. Vedas=Required external sacrifices (crops, animals, etc.)
Upanishads =Required internal sacrifices. (ego, fruit of actions)
E. Yoga = The path of renunciation
F. Maitrayania Upanishads- This text dates from the second or third century
B.C.E. In this upanishad yoga is defined as a means of binding or controlling the breath and the mind using the syllable Om. This Upanishad states that The oneness of the breath and the mind, and likewise the senses, and the relinquishment of all conditions of existence is designated as yoga.
G. Sixfold Path- breath control (pranayama) , withdrawal of the senses (pratyahara), meditation (dhyana), concentration (dharana), contemplation (tarka), and absorption (samadhi). These are the first vital elements of yoga and they would be expanded later in the second century C.E., in Patanjali's Yoga Sutra.
H. Bhagavad Gita- a contemporary of the Ramyana, and although written after the Mahabharata, It is at its core believed to be much older. It proposes a three prong approach to liberation consisting of: karma yoga, the path of service; jnana yoga, the path of wisdom or knowledge; and bhakti yoga, the path of devotion.
I. Samkhya- 400 and 200 B.C.E. and was begun by a sage named Kapila. Kapilas philosophy so radical is that he believed that the visible world was not a manifestation of the Divine. Suffering, occurred when one became attached to things that were not the self. What got passed on from Samkhyan's school was the idea that there are two separate forms of reality, one called (purusha) and the other called (prakriti). Purusha is all-knowing, without beginning and without ending, it has no features or characteristics and it is thought to exist without motion or form as pure consciousness, and it was considered to be male. Praktriti, on the other hand, was thought to be female and in constant motion, active, distinct, creative and formative, but entirely unconscious. These are the qualities that were assigned to all of nature and the material world. Praktri was the female principle which created everything through the manifestations of her nature. These manifestations of her nature are called gunas.
J. Gunas- Praktri was the female principle which created everything through the manifestations of her nature. These manifestations of her nature are called gunas. In the early history of Samkyhan system these gunas were thought to be neutral manifestations pf prakriti: only later did the gunas take on more definite qualities. The idea of gunas was adopted by both the Upanishads and the Bhagavad Gita.
Sattva- The guna of the mind and the cognitive senses (skin, tongue, nose, eyes and ears) The cognitive senses keep us connected to the external world and the mind coordinates all biological and psychic activities.
Rajas- The guna of gross motor responses and physical experience in general. The hands, feet, anus, genitals, and the voice are thought to be the senses of yearning, these would become active when this guna predominated. Rajas make physical experience possible as it controlled the activity of the body.
Tamas- The guna of darkness and inertia, it gives rise to the structure of existence. It activates the potential of the five subtle elements or senses which are, sight, sound, smell, taste and touch.
K. Duality-Yoga then borrowed it's dualistic cosmological system from the Samkhya tradition, they began to believe that Prakriti dynamically creates everything material and Purusha passively illuminates it all.
L. Renunciation-Later schools of yoga began to believe that the only way out of this erroneous attachment to objects and desire for sensual gratification was for the yogi or adept to completely renounce the world. The yogi would have to renounce all attachment to (pratriti) or the natural world if he wanted to experience the ultimate state of universal consciousness or (purusha).

Classical Yoga (100B.C.E.- 500C.E.)
A. Patanjali- Indian philosopher who lived in the second century c.e., he is credited for authoring the first systematic presentation of yoga called the Yoga Sutra. Patanjali succeeded in bringing together all the written and oral knowledge of his time into a collection of 195 sutras (aphorisms or 'terse statements') which included information on everything a yoga teacher needed to teach yoga, from how to conduct oneself in society to final enlightenment. These sutras were meant to assist the guru or teacher in his task of teaching spiritual liberation. Patanjali was a follower of the Samkhya school before him, and so took a dualist view of reality. Patanjali believed, like the Samkhya philosophers before him, that human suffering was the result of becoming attached to external phenomenon. He believed that desire and passion kept mans psyche enslaved and distracted by the phenomenal world and that only by renouncing that world could he ultimately attain enlightenment. Suffering was thought to be produced by the conflict between the gunas within the human psyche. Patanjali believed though that there was a way out of this suffering, that through hard work (karma yoga) and deep meditation (jnana yoga) suffering could be relieved and liberation or enlightenment could take place, Patanjali devised a system called the eight -limbed path of yoga (astanga yoga) to bring the gunas back into balance. In his Yoga Sutras presented a version of kriya yoga, kriya yoga is an internal form of karma yoga. That is by perfecting niyamas (self disciplines) of the eight limbed path, particularly the tapas (austerity), svadhyaya (self-study), isvara pranidhana (devotion to the Lord) a yogi could erase samskara (subliminal activators) from his subconscious mind. it was believed that samskara were like karma scares that resulted from good or bad behavior.
B. Yoga Sutra- comprises four books:
Samadhi Pada which explains the final goal of yoga, the object of practice, as well as its results and effects.
Sadhana Pada deals with the practice of yoga or sadhana.
Vibhuti Pada which indicates how the results of our practice (sadhana) manifest.
Kaivalya Pada: The state of union with the Self, how it is lived in our life. One will perceive that all actions come from the Soul, experiences inner piece, happiness and balance, which constitute the principal object of creation.
C. Eight Limbs- The 195 sutras (words of wisdom) that comprise the Yoga Sutra expound the practice of yoga into an eight-limbed path of self transcendence, these are:
Yama – Self-restraint or ethical conduct
Niyama – Personal and religious observance of purity, devotion and study
Asana – Physical activity
Pranayama – Breath control or regulation
Pratyahara – Abstraction of the senses
Dharana – Concentration
Dhyana – Meditation that leads to Samadhi
Samadhi – Absorption in the sublime and blissful awareness.

Patañjali's concept was prevailing for some centuries that some Yogis focused entirely on Meditation and ignored the practice of Asanas>
D. Inconsistency of Dualistic Philosophy:
The plurality of souls (purushas)
Since the self in Samkhya-Yoga metaphysics is devoid of any attributes that could individualize it, no difference can be made between one purusha and another, and therefore their plurality is problematic. S. Radhakrishnan writes:
The self is without attributes or qualities, without parts, imperishable, motionless, absolutely inactive and impassive, unaffected by pleasure or pain or any other emotion. All change, all character belong to prakriti. There does not seem to be any basis for the attribution of distinctness to purushas. If each purusha has the same features of consciousness, all-pervadingness, if there is not the slightest difference between one purusha and another, since they are free from all variety, then there is nothing to lead us to assume a plurality of purushas. Multiplicity without distinction is impossible (Indian Philosophy, vol. II, p. 322).
The incompatibility between empirical and absolute knowledge
As a result of the opposed nature of purusha and prakriti, the Samkhya-Yoga metaphysics encounters problems in establishing harmony between empirical and absolute knowledge. Here is how S. Radhakrishnan comments on this puzzling aspect:
When the Samkhya breaks up the concrete unity of experience into the two elements of subject and object and makes them fictitiously absolute, it cannot account for the fact of experience. When purusha is viewed as pure consciousness, the permanent light which illuminates all objects of knowledge, and prakriti as something opposed to consciousness and utterly foreign to it, the latter can never become the object of the former. The Samkhya cannot get across the ditch which it has dug between the subject and the object. [...] Unless the subject and object are akin to each other, how can the one reflect the other? How can buddhi, which is non-intelligent, reflect purusha? How can the formless purusha which is the constant seer be reflected in buddhi which is changing? The two cannot, therefore, be absolutely opposed in nature (Indian Philosophy, vol. II, p. 303-4).

No possible relationship can exist between empirical knowledge, which belongs to the domain of prakriti, and the absolute knowledge of purusha. Because they belong to different realms, on the one hand purusha cannot know prakriti, and on the other hand, prakriti and all its forms cannot do anything to help liberation.
An attempt to solve this difficulty was made by postulating the fact that prakriti operates instinctively for purusha's liberation. The Samkhya-Sutra (3,47) states that "creation (prakriti) works for the sake of purusha, so that it may attain supreme knowledge." The Yoga-Sutra of Patanjali (2,21) also mentions that prakriti exists only for the sake of serving purusha's liberation. But in the absence of an external agent who could "inspire" a teleological instinct to prakriti, the difficulty is not solved. Samkhya rejects the existence of a creator god, and Ishvara of the Yoga darshana is not a personal god, but rather a macro-purusha that was never involved with psycho-mental activity or the law of karma (Yoga-Sutra 1,24), being devoid of any creative abilities.
The teleological instinct of prakriti was illustrated in the Samkhya and Yoga darshanas by the image of a horse that pulls a wagon out of instinct, an act to which the wagon driver is a simple spectator. In the same way, prakriti would conduct purusha toward liberation without any external directive. However, it is omitted in this metaphor that the horse was first trained by the driver before he knew the way home. Samkhya metaphysics does not allow such an external "coach" for prakriti. Another deficient illustration used by the Samkhya followers is that of a blind man and a lame man helping each other on their journey. Neither can this be a valid illustration to symbolize the teleological instinct of prakriti, since both the blind man and the lame man possess intelligence and language, and therefore can cooperate in realizing a common purpose. Such cooperation between purusha and prakriti cannot exist, because they have nothing in common. Therefore, the difficulty generated by the impossible relationship between purusha and the psycho-mental abilities cannot be properly solved. How could intellect help to distance purusha from prakriti, if intellect itself is a category of prakriti?
Liberation as isolation
Personhood is considered to be a product of prakriti's manifestation, a sum of psycho-mental experiences that cease to exist at the moment of liberation. Instead of the pantheist view of liberation, consisting of an impersonal merging of the self with the Absolute, the Samkhya and Yoga darshanas state that the liberated self (purusha) remains eternally isolated, devoid of any relation with other purushas (or with Ishvara, in Yoga) and having as the only possibility that of knowing itself. But given the fact that purusha is devoid of any personal attributes, it is hard to grasp what this self-contemplation could mean. As in pantheism, liberation is out of personhood, it does not mean becoming a free person.

Post Classical Yoga (500 - 1700C.E.)
A. Non-duality- a view that suffering ceases when you understand that the Self is not separate, but an integral part of the transcendent self (atman).
B. Tantra Yoga- 4th Century CE
Opposite of renunciation
Rejected the Vedas
Refuted the notion that liberation could only be gained by Ascetism and meditation.
Believed in Bhakti yoga and worship of the Goddess. Unlike its predecessors it held the feminine in high regard.
Feminine is related to nature (prakriti)
Suffering is relieved by unifying opposites.
Tantra celebrated the body and promoted a strong healthy body.
The body was the sacred temple for the Divine, and the vehicle for attainment of liberation.
Like earlier Upanishadic yoga, the whole world is not an illusion, but a manifestation of the divine.
Tantrikas adhere to the Yamas and Niyama as well as Asana, pramnayama and pratyahara as set in the yoga sutra. From there the single focus is on a diety.

Two Schools
Right Hand= symbolic
Left Hand= Literal
Socially questionable in rituals.
5 M's
Madya - wine
Matsya - Fish
Mamsa - meat
Mudra - parched grains
Maithuna - sexual intercourse

Tantra also ritually used Mantras, Mandalas, mudras in there practices.
Tantric Yoga began the exploration into the physical experience by focusing on not only the physical but subtle energetic body. It is at this time that we are introduced to the Chakras, Prana, Nadis, Grantis, Kundalini shakti.
Bhakti Yoga- Yoga of devotion. In Tantra, Goddess (female, Shakti ) worship.
C. Purusha=Shiva and resides in the body.
Prakriti=Shakti and resides at the base of the spine.
Liberation comes when there is a unity of these two energies.
D. Hatha Yoga- 9-10century ce)
Non-dualistic. - Joining of opposites Sun moon - forceful yoga.
Follow Ashtanga Yoga (patanjali)
Took best of Tantra yoga and left other culturally offensive rituals behind.
Considered a radical sect for focusing on the body and paranormal powers.
Matseyandra & Goraksha- father of Hatha yoga
Svatmarma writes Hatha yoga pradipika
Asana and pranayama becomes king

More exploration of the body
Purification rituals- neti, nauli, etc.
5 sheaths = Koshas

Modern Yoga (1700- present)
A. Arrives Late 1800 in west. It can be attributed to many gurus, including Swami Vivekananda, a student of Ramakrishna who was commissioned to attend the 1893 Parliament of Religions in Chicago causing deep impression on the Americans. Other important Yoga gurus include Swami Paramahansa Yogananda, Swami Sivananda Radha, Sri Tirumalai Krishnamacharya, Yogi Swami Sivananda, Swami Satchidananda and Maharishi Mahesh Yogi who popularized Transcendental Meditation in the 1960's.
B. Hatha Yoga Poses- The physical poses of Hatha Yoga have a tradition that goes back to the 9th century, but they were not widely practiced in India prior to the early 20th century. Hatha Yoga was advocated by a number of late 19th to early 20th century gurus in India, including Sri Krishnamacharya in south India, Swami Sivananda in the north, Sri Yogendra in Bombay, and Swami Kuvalyananda in Lonavala.
T. Krishnamacharya- Foremost influencer of modern yoga. His students styles of yoga practice form the basis for most of modern yoga practiced today in the west. Four listed below are all his students.
Patthabi Jois- Founder of Ashtanga Vinyasa Yoga.
BKS Iyengar- Son in Law of T. Krishnamacharya. Founder of Iyengar Yoga.
T.K.V. Desikachar- Son of T. Krishnamacharya. Founder of Viniyoga
Indra Devi- Latvian woman trained by T. Krishnamacharya.

Around 800 B.C.E. the age of philosophy arose almost simultaneously throughout the ancient world. In Greece, the Middle East, India, and China the sages, who were always the inward-looking began to think about the way we think. Prior to this time, all religious practices were outwardly focused. The tools of religion, the rituals, and sacrifices were designed to barter and bargain with the elements of nature and the gods. The assumption was - if we conducted these sacrifices for the benefits of the gods, they would be pleased, and in turn would do us favors. The favors sought were of three kinds: rewards of health, wealth, and progeny. We all want to be healthy, to have lots of money, and lots of children. Enlightenment, three thousand years ago, was not a goal. At best one might hope to be taken to a heavenly reward after this life, but even this was a later religious invention.

With the dawning of philosophy, the focus turned inward. The external powers of nature were seen as reflections of the inner world, and vice versa. External sacrifices and rituals became internalized. No longer were the gods out there; they were metaphors for what was happening in here. No longer did you need a priest to talk for you to the divine - the divine already resided inside you; you needed to do the work yourself. A map to self-realization, or more correctly Self-realization, was required to help guide you on the path, but you had to walk the path. One such map became very influential in India around the time of the Buddha. It explained the inner and outer workings of the mind and the world. While the map didn't answer all the questions, and everyone did not accept some of the answers it did produce, it was the most comprehensive model yet devised. It became the foundation for yogic and Buddhist cosmology. It was the Samkhya psychocosmological model.

We will leave it to the historians to argue whether Samkhya created this model, and thus can be considered the father of the yogic model that followed it, or whether there was an earlier version from which both Samkhya and yoga evolved, thus making the two brothers, rather than father and son. For our purposes it is enough to know that both Samkhya and Classical Yoga, from which all other yoga's evolved (especially the Tantra and Hatha yoga's most practiced today), share this same psychophysical view of the universe.

Samkhya and the Classical Yoga of the Yoga Sutras are dualistic philosophies. In the Samkhya tradition there is purusha and there is prakriti. Purusha is the soul, the Self, pure consciousness, and the only source of consciousness. The word literally means "man." Prakriti is that which is created. It is nature in all her aspects. Prakriti literally means "creatrix," the female creative energy. Unlike in the Western religions, purusha did not create prakriti; in fact, if given a choice, purusha would prefer to have never met prakriti at all. But purusha is responsible for prakriti becoming animated, alive. Samkhya philosophy holds that there are countless individual purushas, each one infinite, eternal, omniscient, unchanging, and unchangeable. There is no single purusha that sits hierarchically above any others. There is no creator god, no puppet master pulling any strings. Since purusha is pure consciousness, it follows that prakriti is unconscious. Prakriti is everything that is changing. Prakriti is not just the physical aspects of the universe that we can sense; it is our very senses themselves - our thoughts, memories, desires, and even our intelligence. Prakriti is everything that is that isn't conscious. Consciousness resides only in purusha, or more properly, as purusha. Purusha, pure and distant, is beyond subject and object. One cannot understand purusha, for that would make it an object. Purusha cannot know or understand anything either, for that would make purusha a subject. Purusha simply just is. But, because of the presence of prakriti, purusha gets attracted to nature in the way a man is attracted when he watches a beautiful woman dancing. He cannot help but try to get closer. And then the disaster occurs: purusha becomes trapped inside prakriti. The liberating of purusha from prakriti comes through the practice of yoga.

Samkhya theorizes that Prakriti is the source of the world of becoming. It is pure potentiality that evolves itself successively into twenty four tattvas or principles. The evolution itself is possible because Prakriti is always in a state of tension among its constituent strands
Sattva - a template of balance or equilibrium;
Rajas - a template of expansion or activity;
Tamas - a template of inertia or resistance to action.

All macrocosmic and microcosmic creation uses these templates. The twenty four principles that evolve are Manas or "Antahkaran" evolves from the total sum of the sattva aspect of Pañca Tanmatras or the "Ahamkara" Prakriti - The most subtle potentiality that is behind whatever is created in the physical universe, also called "primordial Matter". It is also a state of equilibrium amongst the Three Gunas. Mahāt - first product of evolution from Prakriti, pure potentiality. Mahat is also considered to be the principle responsible for the rise of buddhi or discriminatory power (wisdom) in living beings. Ahamkāra or ego-sense - second product of evolution. It is responsible for the self-sense in living beings. It is also one's identification with the outer world and its content. "Pañca Tanmātrās" or five objects (color, sound, smell, taste, touch) are a simultaneous product from Mahāt Tattva, along with the Ahamkāra. They are the subtle form of Pañca mahābhūtas which result from grossification or Panchikaran of the Tanmatras. Each of these Tanmatras are made of all three Gunas. Pañca jñāna indriyas or five sense organs (eyes, ears, nose, tongue and body) - also evolves from the sattva aspect of Ahamkara. Pañca karma indriyas or five organs of action - The organs of action are hands, legs, vocal apparatus, urino-genital organ and anus. They evolve from the rajas aspect of Ahamkara. Pañca mahābhūtas or five great substances - earth, water, fire, air and ether. They evolve from the "tamas" aspect of the "Ahamkara". This is the revealed aspect of the physical universe.

Samkhyan cosmology describes how life emerges in the universe; the relationship between Purusha and Prakriti is crucial to Patanjali's yoga system. The strands of Samkhyan thought can be traced back to the Vedic speculation of creation. It is also frequently mentioned in the Mahabharata and Yogavasishta.

Excerpts from and Wikipedia.

Breath and Energy
When we breathe in there is a subtle sound which is known as 'So' and when we breathe out there is a subtle sound which is known as 'Ham' Everyone can experience this with slight practice. This sound of 'Soham' is continuously going on with every breathing. In a period of one day, that is twenty-four hours, we take 21.600 breathings. That means this type of sound which is known as Mantra, is being continued in our body for that many number of times (21.600). If the yogi observes this mentally and consciously, this becomes a great Sadhana. A Sadhana is a discipline undertaken in the pursuit of a goal. Abhyāsa is repeated practice performed with observation and reflection. Kriyā, or action, also implies perfect execution with study and investigation. Therefore, sādhana, abhyāsa, and kriyā all mean one and the same thing. A sādhaka, or practitioner, is one who skillfully applies...mind and intelligence in practice towards a spiritual goal. The most important aspect of the Yoga Sadhana of Jnaneshvara is the activation of the Kundalini Shakti. This is a Tantric Sadhana of the Nath Cult. Jnaneshvara has given a detailed account of this process in his sixth chapter. This is a practical application of the philosophy of Nath Panth. They say that the whole universe is created out of the energy of Shiva or Mahashiva or Adinatha. They call it Shakti or cosmic energy. This energy is occupying the whole universe. The smallest portion of this energy is known as Kundalini, and the energy which is present in the entire universe is known as Maha Kundalini. This energy is present in human beings in potential form (Supta Shakti).

The Yogis who have experienced this energy, say that this is like a serpent and is situated at the end of the Shushumna Nadi in a coiled form, in three and a half coils, position. This also is in line with their philosophy which says "Bramhandi te Pindi". This means that whatever exists in the universe also exists in the human being in the subtle form. This energy can be activated by Mantra Yoga, Laya Yoga and Bhakti Yoga.

The ultimate stage of realisation or Moksha is the union of Shakti with Shiva. Hence the yogi has to activate this energy and allow this energy to go through all the six chakras gradually. The place of Shiva is considered to be in the last chakra which is known as Sahasrara. In the ultimate stage, Sadhaka has to transfer this energy to this last chakra. This is supposed to be the point of union of Shakti with Shiva. One who is successful in this process, is supposed to be a great Yogi. A number of spiritual powers known as siddhis are at his disposal in that stage. A number of examples are available in the ancient Shastras about the Yogis, who were successful in obtaining this highest stage.

Exerpt from wikipedia.