These actions, which remove the impurities of the mind, and thus gradually increase the lustre of knowledge, until the final state of supreme knowledge is acquired, are called kriyāyoga. They are also called yogāṅgas, as they help the maturity of the Yoga process by gradually increasing the lustre of knowledge. They represent the means by which even an ordinary mind (_vikshiptacitta_) may gradually purify itself and become fit for the highest ideals of Yoga. Thus the _Bhāshya_ says: “By the sustained practice of these yogāṅgas or accessories of Yoga is destroyed the fivefold unreal cognition (_avidyā_), which is of the nature of impurity.” Destruction means here disappearance; thus when that is destroyed, real knowledge is manifested. As the means of achievement are practised more and more, so is the impurity more and more attenuated. And as more and more of it is destroyed, so does the light of wisdom go on increasing more and more. This process reaches its culmination in discriminative knowledge, which is knowledge of the nature of purusha and the guṇas. CHAPTER XII THE YOGĀṄGAS Now the assertion that these actions are the causes of the attainment of salvation brings up the question of the exact natures of their operation with regard to this supreme attainment. Bhāshyakara says with respect to this that they are the causes of the separation of the impurities of the mind just as an axe is the cause of the splitting of a piece of wood; and again they are the causes of the attainment of the supreme knowledge just as dhaṛma is the cause of happiness. It must be remembered that according to the Yoga theory causation is viewed as mere transformation of energy; the operation of concomitant causes only removes obstacles impeding the progress of these transformations in a particular direction; no cause can of itself produce any effect, and the only way in which it can help the production of an effect into which the causal state passes out of its own immanent energy by the principles of conservation and transformation of energy, is by removing the intervening obstacles. Thus just as the passage of citta into a happy state is helped by dharma removing the intervening obstacles, so also the passage of the citta into the state of attainment of true knowledge is helped by the removal of obstructions due to the performance of the yogāṅgas; the necessary obstructions being removed, the citta passes naturally of itself into this infinite state of attainment of true knowledge, in which all finitude is merged. In connection with this, Vyāsa mentions nine kinds of operation of causes: (1) cause of birth; (2) of preservation; (3) of manifestation; (4) of modification; (5) knowledge of a premise leading to a deduction; (6) of otherness; (7) of separation; (8) of attainment; (9) of upholding (_Vyāsabhāshya_, II. 28.)