Non-difference, this word not to be found in the English Dictionary is the nearest English translation of the Sanskrit word, Abheda. The word, Abheda, means non-existence of difference. In Vedanta philosophy this word plays a vital role in explaining the indicatory mark in respect of the unity of the individual self with the Infinite or Brahman.
Audolomi (Brahma Sutra I.iv.21) is believed to have held the view that the individual self differs from the supreme self while it possesses a body, but when a man obtains the clear knowledge by means of practice and meditation, dies, leaves the body and obtains complete liberation, the individual self becomes the supreme self, which means in liberation, there is no difference; in transmigration, there is difference; the absolutely different individual self becomes identical in the state of liberation. This is the non-identity non-difference theory of Audolomi. However, Kasakrtsna (Brahma Sutra I.iv.22) believed that the very supreme self exists as the individual soul without undergoing any change which view-point is supported by Badarayana when he reiterates that the individual is only an apparent part of the partless Brahman; the difference is imaginary. This is the non-duality non-difference theory of Kasakrtsna. In his commentary on the Brahma Sutra II.i.14 Adi Sankara explains that the difference between the 'experiencer' and the 'things experienced' which is observed in common experience, in reality does not exist, there is non-difference of cause and effect for all things are merely modifications, and "a modification has speech as its origin and exists only in name" (Chandogya Upanishad VI.i.4), and "All this has That as its essence; That is the Reality; That is the Self; That thou art" (Chandogya Upanishad Vi.vii.7); "All this is but the Self" (Chandogya Upanishad VII.xxv.2). Difference commonly observed is the creation of ignorance whereas non-difference is natural; when the individual ignorance is destroyed through knowledge unity with Self is attained – "Anyone who knows that supreme Brahman becomes Brahman indeed" (Mundaka Upanishad III.ii.9), "Being but Brahman, he is absorbed in Brahman" (Brhadaranyaka Upanishad IV.iv.6).