Hatha Yoga Pradipika examining Buddhist tantric commentaries and medieval yoga texts that came before the "Hatha Yoga Pradīpikā", Birch found that the adverbial uses of the word suggests that it meant "force". Birch found that, "Rather than the metaphysical explanation of uniting the sun (ha) and moon (ṭha), it is more likely that the name haṭha yoga was inspired by the meaning 'force'." Hatha Yoga Pradipika The Hatha Yoga Pradīpikā ( or Light on Hatha Yoga) is a classic fifteenth-century Sanskrit manual on hatha yoga, written by "Svāmi" Svātmārāma, who connects the teaching's lineage to Matsyendranath of the Nathas. It is among the
Aparoksha from which unity of existence is derived. This knowledge is gained by establishing a "guru-shishya sambandha" (Guru-shishya tradition) with a teacher who has already experienced that kind of knowledge (Aparoksanubhuti); the karma or acts required to be done, after gain of "Aparoksha jnana" is "Vidya-karma" which consists in "sravana" (hearing of srutis), "manana" (reflection) and "nididhyasana" (meditation on Brahman). Aparoksha is "savikalpa jnana" (knowledge) when one re-recognizes the non-dual nature of the ever-realized Self (Tat Tvam Asi), it is the immediate knowledge gained through the "pramanas"; practice of "Dhyana" (meditation) removes all "vikalpas" (varied thoughts) and leads to "nirvikalpa" or