In pre-modern India, various yogic schools existed. One summation and systematization of these traditions is found in the Yoga Sutras of Patanjali, generally dated between the 1st and 4th Centuries CE. This document eventually gained canonical status, such that Patanjali’s sutras, and early commentaries on them, became authoritative for the subsequent yogic tradition. In these sutras, Patanjali defines yoga as follows:
"Yoga is the stilling of the changing states of the mind.
When that is accomplished, the seer abides in its own true nature."
This meditative form of yoga is sometimes referred to as raja, or “royal,” yoga, in contrast to wider meanings of the term used in other contexts. Edwin Bryant, a Western authority on the yogic tradition, comments as follows:
"According to Patanjali's definition in the second sutra, yoga is the cessation of the activities or permutations (vrttis) of the citta. The vrttis refer to any sequence of thought, ideas, mental imaging, or cognitive act performed by the mind, intellect, or ego as defined above – in short, any state of mind whatsoever. It cannot be overstressed that the mind is merely a physical substance that selects, organizes, analyzes, and molds itself into the physical forms of sense data presented to it; in an of itself it is not aware of them. Sense impressions or thoughts are imprints in that mental substance, just as a clay pot is a product made from the substance of clay, or waves are permutations of the sea. The essential point for understanding yoga is that all forms or activities of the mind are products of prakrti, matter, and completely distinct from the soul or true self, purusa, pure awareness or consciousness.
The citta can profitably be compared to the software, and the body to the hardware. Neither is conscious; they are rather forms of gross matter, even as the former can do very intelligent activities. Both software and hardware are useless without the presence of a conscious observer. Only purusa is truly alive, that is, aware or conscious. When uncoupled from the mind, the soul, purusa, in its pure state, that is, in its own constitutional, autonomous condition – untainted by being misidentified with the physical coverings of the body and mind – is free of content and changeless; it does not constantly ramble and flit from one thing to another the way the mind does. To realize pure awareness as an entity distinct and autonomous from the mind (and, of course, the body), thought must be stilled and consciousness extracted from its embroilment with the mind and its incessant thinking nature. Only then can the soul be realized as an entity completely distinct from the mind (a distinction such cliches as "self-realization" attempt to express), and the process to achieve this realization is yoga...
Through grace or the sheer power of concentration, the mind can attain an inactive state where all thoughts remain only in potential but not active form. In other words, through meditation one can cultivate an inactive state of mind where one is not cognizant of anything. This does not mean to say that consciousness becomes extinguished, Patanjali hastens to inform us (as does the entire Upanishadic/Vedantic tradition); consciousness is eternal and absolute. Therefore, once there are no more thoughts or objects on its horizons or sphere of awareness, consciousness has no alternative but to become conscious of itself. In other words, consciousness can either be object-aware or subject aware (loosely speaking). The point is that it has no option in terms of being aware on some level, since awareness is eternal and inextinguishable. By stilling thought, meditation removes all objects of awareness. Awareness can therefore now be aware only of itself. It can now bypass or transcend all objects of thought, disassociate from even the pure sattvic citta, and become aware of its own source, the actual soul itself, purusa. This is self-realization (to use a neo-Vedantic term), the ultimate state of awareness, the state of consciousness in which nothing can be discerned except the pure self, asamprajnata-samadhi. This is the final goal of yoga and thus of human existence."
Thus yoga, according to Patanjali, is not a system of physical movement, but rather the stilling of the mind. In fact, in the entire text, a grand total of two verses (2:46-47) are given to asana (posture). The most profound thing Patanjali has to say about posture is that it should be “steady and comfortable.” The purpose of physical yoga is simply to prepare the aspirant to sit in a way that will not cause disturbance during long periods of meditation.
Actual yogic meditation seems to involve concentration (see vs. 1:13: “Practice is the effort to be fixed in concentrating the mind") on one of a wide array of possible objects. Patanjali addresses meditative practice at the end of chapter one of the Sutras, and recommends several options for objects of concentration:
He first recommends repeating the mystical symbol om, which represents Isvara – the personal aspect of God (1.28-1.29).
"Its (the mystical symbol om) repetition and the contemplation of its meaning should be performed. From this comes the realization of the inner consciousness and freedom from all disturbances (changing states of mind)."
But other objects of meditation may also be used, depending on the personality of the meditator. Thus:
"Practice of fixing the mind on one object should be performed in order to eliminate these disturbances." (1.32)
"Or stability of mind is gained by exhaling and retaining the breath." (1.34)
"Or else, focus on a sense object arises, and this causes steadiness of mind." (1.35)
"Or the mind becomes steady when it has one who is free from desire as its object." (1.37)
"Or steadiness of the mind is attained from meditation upon anything of one's inclination." (1.39)
Bryant makes the following comment on Patanjali's objects of meditation:
"Sutra 1.32 indicated that the obstacles to yoga can be overcome by fixing or concentrating the mind on an object, and the next few sutras outline various options and methods for accomplishing this. Patanjali has already presented Isvara as an object of concentration in the form of recitation of the sound om, and by placing Isvara first on the list of options and dedicating so many sutras to him, Patanjali has clearly prioritized an Isvara-centered form of meditation. The following sutras up to 1.39 all also contain the particle va, or. Thus they are all alternative and optional techniques for fixing the mind and, as with the Isvara verses, are to be read as referring back to 1.32, that practice on one object eliminates the distractions to yoga. One or more of them might be more suitable to a particular person, time, and places, says Sankara, hence the options."
Yogic meditation is thus a concentration practice. The recommended object of concentration is Isvara (“God”), represented by the divine sound om, but may change depending on the disposition of the meditator.