The functional area for language is the material world, which can be expressed in the affirmative mode (in the mode of 'is'), but the pure state of soul cannot be expressed through the affirmative linguistic approach. So its manifestation in Ācārāṅga, Upaniṣad and other scriptures takes place in the language of negation (neti neti).
The style used in the āgamic age for the expression of the nature of soul is similar to that of Upaniṣad's negation style. The sound, colour, smell, taste and touch are not the qualities of soul.[1] The soul itself does not have any form while expressing the pure nature of the soul, all these are negated. Thus its narrative language is in negation.
Sānkhya philosophy has also expounded the pure nature of the soul, so when the Jain āgama describes the pure state of soul, it comes close to the Sānkhya philosophy. However, the difference is that Sānkhya philosophy considers soul to be always pure and non-changing whereas, the Jain philosophy believes in the soul's impure state and that it always undergoes transformations.
'kusale puṇa ṇo baddhe ṇo mukke[2]' - [man of wisdom does not get bound nor get liberated], such statements are available in the āgamic literature but in the post philosophical literature of Jainism, the voices of such expressions became weak. The soul had also been explained in the Jain philosophical scriptures but its style of expression had changed. The description of soul's pure state is not available there. The description of soul's pure state is available, either in the āgamic age literature or in the literature like Samayasāra and other scriptures that are close to the āgamic age. The soul's idea propounded with the niścaya naya of the āgamic literature comes closer to the idea of soul of Sānkhya philosophy and negatively expressed idea of soul come closer to the idea of soul as described in Upaniṣad. As Acārāṅga considers the soul non-apprehensible by word, logic etc., similarly, Upaniṣads also accepts soul as unperceivable by senses, voice, intellect and mind.