There exists a vast field of knowledge which the seer must cognize at some time or another. It is generally conceded among occult psychologists, that there are three modes of apprehension:

1. Direct cognition through the avenue of the senses, each sense, when in use, putting its user into contact with a distinct range of vibrations, demonstrating as form manifestations.
2. Deduction or inference, the use by the cognizer of the reasoning powers of the mind in [16] relation to that not directly perceived. This is, for the occult student, the use of the Law of Correspondences or of Analogy.
3. The direct cognition of the yogi or seer, centered in the consciousness of the self, the ego on its own plane. This is achieved through the right use of the mind as an organ of vision and transmission. Patanjali says:
   "The seer is pure knowledge (gnosis). Though pure he looks upon the presented idea through the medium of the mind." - Book II, Sutra 20.

Deduction is not a sure method of ascertaining knowledge and the other modifications refer primarily to the wrong use of the image making faculty (imagination), to the self-induced passivity of the mind, a condition of semi-trance, and to the retention of thought forms within the mental aura, through the use of the memory. Each of these is now dealt with in a separate sutra by Patanjali.