Swami Vivekananda on Patanjali

In his book called "Raja Yoga", Swamiji comments on Patanjali Yoga Sutras. In Chapter 4, Verse 1, it states that the Siddhis (powers) are attained by birth, chemical means, power of words, mortification or concentration.

1. Birth. Swamiji says people may be born with powers which they have earned in their earlier incarnations. He opines that Kapila, founder of Sankhya philosophy was one such. Hindus & Christians also believe that  Lord Krishna & Jesus Christ (among others) also had powers from birth.

2. Chemistry began as alchemy & in India there was a sect called Rasayanas, who thought that bodies can even be made immortal so that one has the time to become spiritual. The drug taking of the west is a unwise byproduct of this. Even Aldous Huxley in his "The Doors of Perception" recounted his altered state of consciousness after consuming Mescaline.

3. There are certain sacred words called Mantras, which have power, when repeated under proper conditions to produce these extraordinary powers (e.g. like those used in rituals.)

4. In every religion, mortifications & asceticisms have been practised. Through such practices, it is believed that powers (Siddhis) can be attained.

5. Concentration is Samadhi, & that is Yoga proper; that is the principal theme of this science, & it is the highest means. Here concentration is defined in Chapter 1, Verse 2 as "Yoga Chittavrutti Nirodhaha" meaning "Yoga is restraining the mind-stuff (Chitta) from taking various forms (Vrittis)."