(- the following phrases are said to be phrases of truth)

prajñānam brahma - "Knowledge is Brahman"      (Aitareya Upanishad)

tat tvam asi - "That you are"                         (Chãndogya Upanishad)

aham brahmāsmi - "I am Brahman"              (Bṛhadãranyaka Upanishad)

ayam ātmā brahma - "This Self is Brahman"       (Mãndükya Upanishad)

Ramana Maharshi, in Talk 105, discusses Chandogya Upanishad, Chapter 6, with Madhavaswami. 

(Chandogya references added by MW)

M.: Yena asrutam srutam bhavati (Chandogya Upanishad). (CU 6.1.3 - By which the unheard of becomes heard, the unthought of becomes thought of, the unknown becomes known.) 

Madhavaswami, Bhagavan’s attendant: Are there nine methods of teaching the Mahavakya ‘Tattvamasi’ in the Chandogya Upanishad?

M.: No. Not so. The method is only one. Uddalaka started teaching Sat eva Somya (there is only Being )(cf. CU 6.2.1) illustrating it with Svetaketu’s fast

(1) Sat, the Being in the individual, is made obvious by the fast. (cf. CU 6.7)

(2) This (sat) Being is similar in all, as honey gathered from different flowers. (cf. CU 6.9.1 - 2)

(3) There is no difference in the sat of individuals as illustrated by the state of deep sleep. The question arises - if so, why does not each know it in sleep? (cf. CU 6.8) 

(4) Because the individuality is lost. There is only sat left. Illustration: rivers lost in the ocean. If lost, is there sat? (cf. CU 6.10.1- 2)

(5) Surely - as when a tree is pruned it grows again. That is a sure sign of its life. But is it there even in that dormant condition? (cf. CU 6.11)

(6) Yes, take the instance of salt and water. The presence of the salt in water is subtle. Though invisible to the eye it is recognised by other senses. How is one to know it? What is the other means? (cf. CU 6.13)

(7) By enquiry, as the man left in the Gandhara forest regained his home. (cf. CU 6.14)

(8) In evolution and involution, in manifestation and resolution, sat alone exists. Tejah parasyam, devatayam (the light merges in the Supreme). (cf. CU 6.8.6

(9) An insincere man is hurt by the touch of fire test. His insincerity is brought out by fire. Sincerity is Self-evident. A true man or a Self realised man remains happy, without being affected by the false appearances (namely the world, birth and death, etc.), whereas the false or ignorant man is miserable. (cf. CU 6.16)