Ashtanga, the eight components of yoga
Patanjali defines yoga as having eight components (अष्टाङ्ग aṣṭ āṅga, "eight limbs"):
The eight limbs of yoga are
Yamas are ethical vows in the Yogic tradition and can be thought of as moral imperatives.
The five yamas listed by Yogasūtras are:
The commentaries on these writings of Patanjali state how and why each of the above self restraints help in the personal growth of an individual.
For example, in verse II.35, Patanjali states that the virtue of nonviolence and non-injury to others (Ahimsa) leads to the abandonment of enmity, a state that leads the yogi to the perfection of inner and outer amity with everyone, everything.
In Sutra 2.31, Patanjali calls the Yamas Mahavratam, which means a Great Vow. Patanjali states that practice of the Yamas is universal and it should not be limited by class, place, time or circumstances.
The second component of Patanjali's Yoga path is called niyama, which includes virtuous habits, behaviors and observances (the "dos"). Sadhana Pada Verse 32 lists the niyamas as:
Patanjali begins discussion of Āsana (आसन, meditation posture) by defining it in verse 46 of Book 2, as follows:
sthira sukham asanam॥46॥
Translation 1: An asana is what is steady and pleasant.
Translation 2: Motionless and Agreeable form (of staying) is Asana (yoga posture).
— Yoga Sutras II.46
Asana is thus a posture meditation that one can be hold for a period of time, staying relaxed, steady, comfortable and motionless.
Patanjali does not list any specific asana, except the terse suggestion, "posture one can hold with comfort and motionlessness". Āraṇya translates verse II.47 as, "asanas are perfected over time by relaxation of effort with meditation on the infinite"; this combination and practice stops the quivering of body.
The Bhasya commentary attached to the Sutras, now thought to be by Patanjali himself, suggests twelve seated meditation postures: Padmasana (lotus), Virasana (hero), Bhadrasana (glorious), Svastikasana (lucky mark), Dandasana (staff), Sopasrayasana (supported), Paryankasana (bedstead), Krauncha-nishadasana (seated heron), Hastanishadasana (seated elephant), Ushtranishadasana (seated camel), Samasansthanasana (evenly balanced) and Sthirasukhasana (any motionless posture that is in accordance with one's pleasure).
Prāṇāyāma is made out of two Sanskrit words
prāṇa (प्राण, breath) and
āyāma (आयाम, restraining, extending, stretching).
After a desired posture has been achieved, verses II.49 through II.51 recommend the next limb of yoga, prāṇāyāma, which is the practice of consciously regulating breath (inhalation and exhalation).
This is done in several ways, inhaling and then suspending exhalation for a period, exhaling and then suspending inhalation for a period, slowing the inhalation and exhalation, consciously changing the time/length of breath (deep, short breathing).
Pratyāhāra is a combination of two Sanskrit words prati- (the prefix प्रति-, "against" or "contra") and āhāra (आहार, "food,diet or intake")
Pratyahara means not taking any input or any information from the sense organs. It is a process of retracting the sensory experience from external objects. It is a step of self extraction and abstraction.
Pratyahara is not consciously closing one's eyes to the sensory world, it is consciously closing one's mind processes to the sensory world. Pratyahara empowers one to stop being controlled by the external world, fetch one's attention to seek self-knowledge and experience the freedom innate in one's inner world.
Pratyahara marks the transition of yoga experience from first four limbs that perfect external forms to last three limbs that perfect inner state, from outside to inside, from outer sphere of body to inner sphere of spirit.
Dharana (Sanskrit: धारणा) means concentration, introspective focus and one-pointedness of mind. The root of word is dhṛ (धृ), which has a meaning of "to hold, maintain, keep".
Dharana as the sixth limb of yoga, is holding one's mind onto a particular inner state, subject or topic of one's mind. The mind is fixed on a mantra, or one's breath/navel/tip of tongue/any place, or an object one wants to observe, or a concept/idea in one's mind. Fixing the mind means one-pointed focus, without drifting of mind, and without jumping from one topic to another.
Dhyana (Sanskrit: ध्यान) literally means "contemplation, reflection" and "profound, abstract meditation".
Dhyana is contemplating, reflecting on whatever Dharana has focused on. If in the sixth limb of yoga one focused on a personal deity, Dhyana is its contemplation. If the concentration was on one object, Dhyana is non-judgmental, non-presumptuous observation of that object. If the focus was on a concept/idea, Dhyana is contemplating that concept/idea in all its aspects, forms and consequences. Dhyana is uninterrupted train of thought, current of cognition, flow of awareness.
Dhyana is integrally related to Dharana, one leads to other. Dharana is a state of mind, Dhyana the process of mind. Dhyana is distinct from Dharana in that the meditator becomes actively engaged with its focus. Patanjali defines contemplation (Dhyana) as the mind process, where the mind is fixed on something, and then there is "a course of uniform modification of knowledge".
Samadhi (Sanskrit: समाधि) literally means "putting together, joining, combining with, union, harmonious whole, trance".
Samadhi is oneness with the subject of meditation. There is no distinction, during the eighth limb of yoga, between the actor of meditation, the act of meditation and the subject of meditation. Samadhi is that spiritual state when one's mind is so absorbed in whatever it is contemplating on, that the mind loses the sense of its own identity. The thinker, the thought process and the thought fuse with the subject of thought. There is only oneness, samadhi.
All three (Dhyana, Dharana and Samadhi) practiced on a particular object or subject is called Sanyam by Patanjali.
"Souls on the Banks of the Acheron"
Oil on Canvas, Adolf Hirémy-Hirschl (1898)