Ptanajali is the founder of Yogic Philosophy and is regarded as the complement of Samkhya. The word Yoga means Union i.e. Union of Individual soul to universal soul, and is used in this sense in Vedanta. According to patanjali, Yoga does not mean union but spiritual effort to attain perfection through control of body, senses and mind and through right discrimination between Purusha & Prakriti. Yoga means spiritual action and samkhya means knowledge. For all practical purposes, Samkhya and Yoga may be treated as the theoretical and practical sides of the same  system. The aim of Yoga is to arrest mental modifications (chitta-vritti) so that the self remains in its true, undefiled essence and is, thus, not subject to suffering.

The most important element in Yogic Philosophy is Chitta. First modification of Prakriti in which there is predominance of sattva over rajas or tamas. Due to modifications of chitta according to objects, the self knows different objects.

Acc to Yoga sutras though there is no modification in the self, except as the reflection of the changing Chitta Vrittis, there is an appearance of change in it, just as the moon reflected in the river seems to be moving. When true knowledge is attained, the self ceases to see itself in these modifications of the chitta and gets rid of attachment and aversion to the worldly pleasures and sufferings. The only way to get rid of this bondage is to control the modification of the chitta. The art to control this is called Yoga. 

According to yoga there are several causes of disturbances in the Chitta:

Vyadhi(illness), satyan(lack of interest), sanshya(lack of confidence), pramad(distraction), alasya(laziness), avirti(cravings & desires), bhrantidarshan(illusion & dellusion), Alabdhabhūmikatvā(unable to reach higher state), anavastitatva(unable to maintain highest state).

After the encounter of these basic hindrances, four normal hindrances may be seen according to the situation. They are the consequences of previous obstacles.  In other words, these four are the symptomatic manifestations of above nine antarayas. 

dukha(suffering) daurmanasya(depression) angamejayatva(body tremoring) swasa-praswasa(unbalanced inhalation exhalation)

Yoga prescribed the practice of concentration or one-pointedness to check the above mentioned causes of distractions of chitta. Together with concentration. There should be 

friendliness towards living being (maitri), compassion (karuna), (mudita) gladness or pleasant towards goods, (upeksha)- (indifference) or aversion towards evil

Patanjali lays down an eightfold path consisting of aids to Yoga: restraint (yama), observance (niyama), posture (asana), regulation of breathing (pranayama), abstraction of the senses (pratyahara), concentration (dharana), meditation (dhyana), and trance (samadhi). The first two constitute the ethical core of the discipline: the restraints are abstinence from injury, veracity, abstinence from stealing, continence, and abstinence from greed. The observances are cleanliness, contentment, purificatory actions, study, and surrender of the fruits of one’s actions to God. Ahimsa (nonviolence) also is glorified, as an ethics of detachment.

Various stages of samadhi are distinguished: the conscious and the superconscious, which are subdivided into achievements with different shades of perfection. In the final stage, all mental modifications cease to be and the self is left in its pure, undefiled state of utter isolation. This is freedom (kaivalya), or absolute independence