This word, derived from the root Yuj ("to join"), is in grammar sandhi, in logic avayavashakti, or the power of the parts taken together, and in its most widely known and present sense the union of the jiva, or embodied spirit, with the Paramatma, or Supreme Spirit, and the practices by which this union may be attained. There is a natural yoga, in which all beings are, for it is only by virtue of this identity in fact that they exist. This position is common ground, though in practice too frequently overlooked. "Primus modus unionis est, quo Deus, ratione suæ immensitatis est in omnibus rebus per essentiam, præsentiam, et potentiam; per essentiam ut dans omnibus esse; per præsentiam ut omnia prospiciens; per potentiam ut de omnibus disponens." The mystical theologian cited, however, proceeds to say: "Sed hæc unio animæ cum Deo est generalis, communis omnibus et ordinis naturalis, ., illa namque de qua loquimur est ordinis supernaturalis actualis et fructiva." It is of this special yaga, though not in reality more "supernatural" than the first, that we here deal. Yoga in its technical sense is the realization of this identity, which exists, though it is not known, by the destruction of the false appearance of separation. "There is no bond equal in strength to maya, and no force greater to destroy that bond than yoga. There is no better friend than knowledge (jnana), nor worse enemy than egoism (ahangkara). As to learn the Shastra one must learn the alphabet, so yoga is necessary for the acquirement of tattvajnana (truth)." The animal body is the result of action, and from the body flows action, the process being compared to the seesaw movement of a ghatiyantra, or water-lifter. Through their actions beings continually go from birth to death. The complete attainment of the fruit of yoga is lasting and unchanging life in the noumenal world of the Absolute.

Yoga is variously named according to the methods employed, but the two main divisions are those of the hathayoga (or ghatasthayoga) and samadhi yoga, of which raja-yoga is one of the forms. Hathayoga is commonly misunderstood, both in its definition and aim being frequently identified with exaggerated forms of self-mortification.

The Gherandasanghita well defines it to be "the means whereby the excellent rajayoga is attained." Actual union is not the result of Hathayoga alone, which is concerned with certain physical processes preparatory or auxiliary to the control of the mind, by which alone union may be directly attained. It is, however, not meant that all the processes of Hathayoga here or in the books described are necessary for the attainment of rajayoga. What is necessary must be determined according to the circumstances of each particular case. What is suited or necessary in one case may not be so for another. A peculiar feature of Tan-trika virachara is the union of the sadhaka and his shakti in latasadhana. This is a process which is expressly forbidden to Pashus by the same Tantras which prescribe it for the vira. The union of Shiva and Shakti in the higher sadhana is different in form, being the union of the Kundalini Shakti of the Muladhara with the Vindu which is upon the Sahasrara. This process, called the piercing of the six chakra, is described later on in a separate paragraph. Though, however, all Hathayoga processes are not necessary, some, at least, are generally considered to be so. Thus, in the well-known ashtangayoga (eight-limbed yoga), of which samadhi is the highest end, the physical conditions and processes known as asana and pranayama (vide post) are prescribed.

This yoga prescribes five exterior (vahiranga) methods for the subjugation of the body, namely (1) Yama, forbearance or self-control, such as sexual continence, avoidance of harm to others (ahingsa), kindness, forgiveness, the doing of good without desire for reward, absence of covetousness, temperance, purity of mind and body, etc. (2) Niyama, religious observances, charity, austerities, reading of the Shastra and Ishvara Pranidhana, persevering devotion to the Lord. (3) Asana, seated positions or postures (vide post). (4) Pranayama, regulation of the breath. A yogi renders the vital airs equable, and consciously produces the state of respiration which is favourable for mental concentration, as others do it occasionally and unconsciously (vide post). (5) Pratyahara, restraint of the senses, which follow in the path of the other four processes which deal with the subjugation of the body. There are then three interior (yogangga) methods for the subjugation of the mind, namely (6) Dharana, attention, steadying of the mind, the fixing of the internal organ (chitta) in the particular manner indicated in the works on yoga. (7) Dhyana or the uniform continuous contemplation of the object of thought; and (8) that samadhi which is called savikalpasamadhi. Savikalpasamadhi is a deeper and more intense contemplation on the Self to the exclusion of all other objects, and constituting trance or ecstasy. This ecstasy is perfected to the stage of the removal of the slightest trace of the distinction of subject and object in nirvikalpasamadhi, in which there is complete union with the Paramatma, or Divine Spirit. By vairagya (dispassion), and keeping the mind in its unmodified state, yoga is attained. This knowledge, Ahang Brahmasmi ("I am the Brahman"), does not produce liberation (moksha), but is liberation itself, Whether yoga is spoken of as the union of Kulakundalini with Paramashiva, or the union of the individual soul (jivatma) with the Supreme Soul (paramatma), or as the state of mind in which all outward thought is suppressed, or as the controlling or suppression of the thinking faculty (chittavritti), or as the union of the moon and the sun (Ida and Pingala), Prana and Apana, Nada and Vindu, the meaning and the end are in each case the same.

Yoga, in seeking mental control and concentration, makes use of certain preliminary physical processes (sadhana), such as the shatkarmma, asana, mudra, and pranayama. By these four processes and three mental acts, seven qualities, known as shodhana, dridhata, sthirata, dhairyya, laghava, pratyaksha, nirliptatva (vide post), are acquired.