6.18 यदा when, विनियतम् perfectly controlled, चित्तम् mind, आत्मनि in the Self, एव only, अवतिष्ठते rests, निःस्पृहः free from longing, सर्वकामेभ्यः from all (objects of) desires, युक्तः united, इति thus, उच्यते is said, तदा then.Commentary: Perfectly controlled mind The mind with onepointedness.When all desires for the objects of pleasure seen or unseen die, the mind becomes very peaceful and rests steadily in the Supreme Self within. As the Yogi is perfectly harmonised, as he has attained to oneness with the Self and as he has become identical with Brahman, sense phenomena and bodily affections do not disturb him. He is conscious of his immortal, imperishable and invincible nature.Yukta means united (with the Self) or harmonised or balanced. Without union with the Self neither harmony nor balance nor Samadhi is possible. (Cf.V.23VI.8)