Buddhi constitutes the first level of individuation of the infinitely cognoscent formless brahman into manifest phenomenal reality; the formation (differentiation) of the jivatman from the paramatman. It makes its first scriptural appearance in the Katha Upanishad (I,3) where it is compared in a famous simile to the driver of a horse and carriage, where the reins held by the driver represent the lower mind (manas); the horses represent the five senses and the carriage itself - the body. Ontologically, buddhi is equivalent to hiranyagarbha, and is to individual living souls - jivas - as hiranyagarbha is to the insentient phenomena of the universe. Buddhi is the gateway between the phenomenal and the external. It may, on the one hand, through identification and desire cause the incarnation of brahman into material existence as an individual soul or it may through wisdom (prajna) lead an already incarnate soul to dissolve identification with material phenomena (with cessation of corresponding worldly desires) and become liberated.