The aphorisms about soul available in Upaniṣads have similarity with the aphorisms in Acārāṅga. Both Acārāṅga and Upaniṣads have stated that the pure nature of soul as verbally inexpressible. The soul is non-corporeal and subtlest by nature, so it is not expressible through words. All the words bounce back and cannot even reach up to the soul.[1] In Acārāṅga's Curṇī, the word 'pravāda' has been used.[2] Its meaning is also the same, so as such the soul is not a matter of verbal debate. In Upaniṣad, in the context of Brahma's 'Anand-Vijñāna'(spiritual-bliss), the same statement is available - 'the voice bounce back with mind without reaching the soul.' One who knows the ānand (bliss) of Brahma, does not feel fear anywhere.[3]'
In Acārāṅga, the vastness (cosmos-pervasiveness), tiny form (thumb sized existence) etc. of the soul is categorically negated.[4] It holds that the soul is neither small nor big. In Upaniṣad, the soul has been described as smaller than the smallest and bigger than the biggest in size.[5]
yato vāco nivartante, aprāpya manasā saha
ānandaṃ brahmaṇo vidvān, na bibheti kadācana