But an opponent may here object that "what you formerly stated (p. 147) as to existence being denied of darkness, &c., is surely unreasonable; for, in fact, there are no less than four different opinions maintained on this point,--thus (_a._) the Bháṭṭa Mímáṃsakas and the Vedántins hold that darkness is a substance; (_b._) Śrídhara Áchárya[191] holds that the colour of dark blue is imposed [and thus darkness will be a quality]; (_c._) some of the Prábhákara Mímáṃsakas hold that it is the absence of the cognition of light; (_d._) the Naiyáyikas, &c., hold that it is the absence of light." In reply, we assert that as for the first alleged opinion (_a._) it is quite out of the question, as it is consistent with neither of the two possible alternatives; for if darkness is a substance, it must either be one of the nine well-known substances, earth, &c.,[192] or some different one. But it cannot be any one of the nine, since, under whichever one you would place it, all the qualities of that substance should certainly be found in it; nor can you, on the other hand, assert that it is some substance different from these nine, since, being in itself destitute of qualities, it cannot properly be a substance at all [the very definition of substance being "that which is the substratum of qualities"], and therefore, of course, it cannot be a different substance from the nine. But you may ask, "How can you say that darkness is destitute of qualities, when it is perceived as possessed of the dark blue of the tamála blossom?" We reply, that this is merely an error, as when men say that the [colourless] sky is blue. But enough of this onslaught on ancient sages.[193] (_b._) Hence it follows that darkness cannot have its colour imposed upon it, since you cannot have an imposition of colour without supposing some substratum to receive it;[194] and again, we cannot conceive the eye as capable of imposing a colour when deprived of the concurrent cause, the external light. Nor can we accept that it is an impression independent of the eye [_i.e._, produced by the internal sense, mind], because the concurrence of the eye is not a superfluous but an indispensable condition to its being produced. Nor can you maintain that "absence or non-existence (_abháva_[195]) is incapable of being expressed by affirmative tense affixes [and, therefore, as we _do_ use such phrases as _tenebræ oriuntur_, darkness cannot be a mere non-existence"]; because your assertion is too broad, as it would include such cases of non-existence as a mundane collapse, destruction, inattention,[196] &c. [and yet we all know that men do speak of any of these things as past, present, or future, and yet all are cases of _abháva_]. (_c._) Hence darkness cannot be the absence of the cognition of light, since, by the well-known rule that that organ which perceives a certain object can also perceive its absence, it would follow that darkness would be perceived by the mind [since it is