Why darkness cannot be mere absence of light
In order to know abhAva, we need to have prior knowledge of pratiyogI. (Now please don't bring in the hopeless Eskimo example of SSS ji. That has been analysed and rejected in this group.) For example, in order to know there is pot-abhAva in the room, we need to know what a pot is. Unless we know a pot, we cannot aver that there is pot-abhAva in the room.
When darkness is posited as prakAsha-abhAva, we need to ask whether it is prakAsha-sAmAnya-abhAva or prakAsha-vishesha-abhAva or sarva-prakAsha-abhAva.
That is to say, let there be A = {p1, p2, p3..pn}, which is a set of prakAsha in the universe. Then, the darkness which is posited as prakAsha-abhAva can be either
(i) the abhAva of any of the elements in the set A.
(ii) the abhAva of any specific element in the set A.
(iii) the abhAva of all the elements of the set together.
(iv) the abhAva of each of the elements of the set together.
None of the scenarios are admissible. For example, let us take situation 1 and 2. They are both similar. Let any general or specific element of the set be absent and yet there is sunlight. Can there be darkness? No. Thus, mere absence of a general or specific element of the set does not imply darkness. Hence, it is proved that prakAsha-sAmAnya-abhAva or prakAsha-vishesha-abhAva are not darkness.
Let us take situation 3. This is not tenable either. Because in order to remove darkness, we will need to switch on all p1 to pn. Let us see carefully here: Darkness = abhAva of (p1 ∧ p2 ∧ p3… ∧ pn). So to remove darkness, we need to have p1 & p2 & p3… & pn, which is contrary to experience. Further, it also implies that we must know p1 ∧ p2 ∧ p3… ∧ pn in order to know darkness, which is impossible. Thus, it is proved that darkness is not sarva-prakAsha-abhAva either.
Now, situation 4 states darkness = (~p1 ∧ ~p2 ∧ ~p3 … ∧ ~pn). This implies that in order to know darkness, we need to know each of the p1 to pn. Because unless we know p1, we cannot know p1-abhAva. Thus, similar to situation 3, this situation 4, which demands prior knowledge of all prakAsha, is an impossibility.
Thus, it is proved that darkness is not prakAsha-abhAva.
Another reason
तमः शब्द वाच्यो नाभावः, स्वमात्रवृत्तिधर्मप्रकारकप्रतियोगिज्ञानाजन्यप्रत्यक्षविषयत्वाद्, घटवत्।
(i) There are some particular features of abhAva. It resides at more than one place. For e.g. cloth is pot-abhAva. Table is also pot-abhAva. Thus, pot-abhAva-tva resides in cloth as well as table. However, pot-ness exists only in a pot. It does not exist anywhere else. Thus, pot is a padArtha which is swa-mAtra-vritti-dharma-prakArak. Meaning thereby, its qualitative feature inheres only in it. All non-abhAva-padArtha are similarly swa-mAtra-vritti-dharma-prakArak.
Now, whether darkness-ness is seen anywhere other than darkness? Is it seen in a pot? No. Thus, darkness is also swa-mAtra-vritti-dharma-prakArak.
(ii) The knowledge of an abhAva cannot arise without the knowledge of its pratiyogI. Thus, cognition of abhAva is dependent or causally linked with the cognition of prayogI. Thus, abhAva is always pratiyogI-jnAna-janya.
However, darkness is pratiyogI-jnAna-ajanya. We directly perceive darkness.
(iii) Like a pot, darkness is also an object of pratyaksha.
Thus, just as pot, darkness is swa-mAtra-vritti-dharma-prakArak, pratiyogI-jnAna-ajanya and pratyaksha-vishaya. And there is a vyApti, whichever entity is swa-mAtra-vritti-dharma-prakArak-pratiyogI-jnAna-ajanya-pratyaksha-vishaya, that entity is not abhAVa. तमः शब्द वाच्यो नाभावः, स्वमात्रवृत्तिधर्मप्रकारकप्रतियोगिज्ञानाजन्यप्रत्यक्षविषयत्वाद्, घटवत्।
Thus, we prove through anumAna, which is a valid pramANa, that darkness is not abhAva. Here, darkness is paksha. Hetu is swa-mAtra-vritti-dharma-prakArak-pratiyogI-jnAna-ajanya-pratyaksha-vishaya-tvam. SAdhya is non-abhAva-tva. DrishTAnta is pot.
Another reason
ShankarAchArya says in Brahma Sutra BhAshya 2.2.26 – निर्विशेषस्य त्वभावस्य कारणत्वाभ्युपगमे शशविषाणादिभ्योऽप्यङ्कुरादयो जायेरन् ; न चैवं दृश्यते ; यदि पुनरभावस्यापि विशेषोऽभ्युपगम्येत — उत्पलादीनामिव नीलत्वादिः, ततो विशेषवत्त्वादेवाभावस्य भावत्वमुत्पलादिवत्प्रसज्येत ; नाप्यभावः कस्यचिदुत्पत्तिहेतुः स्यात् , अभावत्वादेव, शशविषाणादिवत्. abhAva does not give rise to anything. On account of being abhAva, like horns of hare. There are no vishesha in abhAva like blue-ness is vishesha in case of lotus. Why? Because on account of this vishesha itself, abhAva will turn to non-abhAva like lotus.
Darkness has a vishesha of black-ness. There is no vishesha in cases of pot-abhAva, cloth-abhAva. Thus, this vishesha itself turns darkness into non-abhAva.
The fact that darkness is not abhAva implies that it is bhAva.
Further, please note that anything which is seen is created and triguNAtmak. So, even if you hold darkness as prakAsha-abhAva, it still is bhAvarUpa because abhAva is also bhAvarUpa as proved by the following anumAna - अपि च, चतुर्विधानामभावानाम् , घटस्येतरेतराभावो घटादन्यो ष्टः — यथा घटाभावः पटादिरेव, न घटस्वरूपमेव । न च घटाभावः सन्पटः अभावात्मकः ; किं तर्हि ? भावरूप एव । एवं घटस्य प्राक्प्रध्वंसात्यन्ताभावानामपि घटादन्यत्वं स्यात् , घटेन व्यपदिश्यमानत्वात् , घटस्येतरेतराभाववत् ; तथैव भावात्मकताभावानाम् ।
Regards.
Sudhanshu Shekhar.