"The Mandukya Upanishad, like the Mundaka and the Prashna and several minor Upanishads, forms part of the Atharva-Veda. It is the shortest of the major Upanishads, containing only 12 verses. Acharya Gaudapada has explained the Upanishad in 250 verses, which are arranged in 4 chapters and are known as the Karika. Shankaracharya has written a highly philosophical commentary (bhashya) on both the Upanishadic text and the Karika, which has been further elucidated by Anandagiri in his notes (tika)...
The Karika, so far as is known at the present time, is the first systematic treatment of Advaita or Nondualistic Vedanta. In it Gaudapada has established nondualism on a philosophical basis. He deals with the subject matter purely on rational grounds (upapatti) independent of scriptural revelation. Devoid of religious, mystical, or scholastic elements, the Karika deals exclusively with philosophy. The one theme running through the Karika is the reality of the nondual and birthless Atman. Shankaracharya, who has commented only on the major Upanishads, the Brahma Sutras, and the Bhagavad Gita, thought it necessary to write a commentary on the Karika, which fact proves its importance in Vedantic literature. The profundity of the Karika easily gives it the status of an Upanishad...
The philosophical method followed in the Karika to arrive at Reality is mentioned in all the major Upanishads. It is known as the analysis of the 3 states (avastha-traya) covering the totality of man’s experience. These are the states of waking, dreaming, and deep sleep. Modern philosophers depend upon experience in order to arrive at true knowledge. They resent the influence of scriptural or supernatural authority. Truth must be based upon facts verifiable by logic. The philosophers of naturalism, empiricism, and logical positivism in the West uphold this position. Gaudapada accepts their point of view but says that the analysis of partial experience gives only a partial truth, whereas total truth demands the investigation of the totality of experience. The physical sciences, psychology, and religion confine their inquiry to the data provided by the waking state, that is to say, to the physical world perceived by the sense-organs. Freud and some other psychologists analyse dreams, not in order to arrive at philosophical truth but merely for the limited purpose of determining the nature of a man’s inhibited tendencies. The study of the phenomenon of deep sleep has not been undertaken at all by Western thinkers, who generally describe it as total unconsciousness and therefore hold it to be meaningless."
- Swami Nikhilananda
"The Upanishad is so named probably after its seer Rishi Mundaka. It belongs to the Atharva Veda group of Upanishads. Of all Upanishads this is the most terse and difficult inasmuch as within the short compass of twelve mantrams, it speaks of the entire range of human consciousness beginning from the awakened state and ending in the Supreme Absolute state of super-consciousness where all objective relations and perceptions of duality are completely negated. According to the Muktikopanishad, it forms the epitome of all the 108 Upanishads which are but elaborations of the contents of the Mandukya. There are very few passages indeed in the authentic Upanishads recognised by the celebrated Bhashyakaras, which unequivocally assert the existence of an Absolute state of consciousness, i.e., Nirguna Atman or Nirguna Brahman, which forms the bed-rock of the grand philosophy of Vivarta Vada or Mayavada as it is commonly known, but herein we have one or two passages which clearly speak of the Nirguna state as the supreme reality. Bhagavan Goudapada, the Paramaguru of Sri Sankaracharya, found this Upanishad as the fit basis for his philosophy of Ajata Vada which he expounded in his Karika on this Upanishad."
- Swami Sharvananda
