So far we have supports for the five senses – the eye consciousness depends on the eye organ, etc. But we don’t yet have one for the mental consciousness. So to keep the scheme consistent, we need a manodhatu, mana-ayatana and a mana-indriya, so that we have the organ/faculty/consciousness triad for each of the six consciousnesses.17c-d. One counts eighteen dhatus with a view to assigning a point of support to the sixth consciousness.
There is then an objection regarding the cessation of the Arhats. Earlier (in 17a-b) the text talked about the continuity of minds from moment to moment. So what happens when the Arhat’s last mind manifests? Does that mean the previous mind didn’t have a subsequent mind? The response is that the absence of a ‘last mind’ isn’t due to some definitional deficiency of manas itself, but because there are no causes, actions or defilements that produce a new thought at that point.
Then we have a couple of helpful summary points:
(Why couldn’t he have started the section by saying this?)(Commentary) All conditioned dharmas are included within the totality of the skandhas; all of the impure dharmas are included within the totality of the upadanaskandhas; and all the dharmas are included within he totality of the aytanas and the dhatus. But, more briefly,
18a-b. All the dharmas are included in one skandhas, one ayatana, and one dhatu.
(Commentary) In rupaskandha, mana-ayatana and dharmadhatu.
18c. A dharma is included in its own nature.
Not in another nature. Why is this?
18d. For it is distinct from the nature of others.
So the commentary clarifies this inclusion point a little. The organ of sight is included within the rupaskandha because it is form, within the sight ayatana and the vision dhatu, within the truth of suffering and arising, but not within the other skandhas, ayatanas, etc.
Then they address briefly the question of whether each individual eye should be counted as a separate organ of sight, and the same for ears, etc.
OK, well that argument is nonsense from a biological, neuroscientific and aesthetic perspective. But it’s consistent with the definitions of the dhatus that we’ve been using so that probably doesn’t really matter.19a-c. The organs of sight, of hearing, and of smell, although twofold, form only, in pairs, one dhatu, for their nature, their sphere of activity, and their consciousnesses are common.
19d. It is for beauty’s sake that they are twofold.
(Commentary) With but a single eye, a single ear, or a single nostril, one would be very ugly.
And that brings us up to the end of this section. I am finding it makes more sense as you go through it: I’m also finding myself wishing he had done the definitions upfront before the analysis.