प्रतिज्ञासिद्धेर्लिङ्गमाश्मरथ्यः ॥ २० ॥
pratijñāsiddherliṅgamāśmarathyaḥ || 20 ||
pratijñā-siddheḥ—Of the proof of the proposition; liṅgam—indicatory mark; āśmarathyaḥ—Asmarathya.
20. (The fact that the individual soul is taught as the object of realization is an) indicatory mark (which is) proof of the proposition, so Asmarathya thinks.
In this Sutra the text quoted in the last Sutra (Brih. 2 . 4. 5) is interpreted from the standpoint of Bhedabheda-vada of sage Asmarathya. According to this school the individual soul (Jiva) and Brahman, which are related as effect and cause respectively, are different, yet not different, from each other, even as sparks are different, yet not different, from fire. If the individual soul (Jiva) were quite different from Brahman, then by the knowledge of the one (Brahman) everything else would not be known. Hence this school interprets the text thus: The individual soul alone is to be seen. But as it is not different from Brahman, the knowledge of the individual soul gives knowledge of Brahman and consequently knowledge of everything. It is this non-difference between Brahman and the individual soul (Jiva) that establishes the proposition, “By the knowledge of one everything else is known”, and in this sense alone the text speaks of the individual soul in Brih. 2. 4. 5.
It can also be interpreted as follows. If the individual soul is something different from Brahman, then the knowledge of Brahman would not give the knowledge of the individual soul. Therefore the individual soul is different, yet not different, from Brahman. It is to show this that the Sruti text begins with the individual soul.