From Nina van Gorkom
Dhammaaramma.na, the sixth class of objects, can be experienced only through the mind-door. It includes all objects other than the sense objects. Dhammaaramma.na can again be subdivided into six classes. They are:
1. The five sense-organs (pasaada-ruupas)
2. The subtle ruuas (sukhuma-ruupas)
6. Concepts and conventional terms (pa~n~natti)
The first class of dhammaaramma.na comprises the five sense-organs (pasaada-ruupas); they are the ruupas which have the capacity to receive sense-impressions. The pasaada-ruupas themselves do not experience anything, they are ruupa, not naama; they function as the doors through which cittas experience objects. The pasaada-ruupas can only be known through the mind-door, not through the sense-doors. For example, we know that there is eyesense, because there is seeing, but we cannot experience eyesense through the eyes.
The five sense-organs are classified as gross (o.laarika) ruupas. Altogether there are twenty-eight kinds of ruupa of which twelve are classified as gross and sixteen as subtle (sukhuma). The gross ruupas include, besides the five sense-organs, the sense objects which can be experienced through the five sense-doors; these are seven ruupas, that is to say: four ruupas which can respectively be experienced through the four sense-doors of eyes, ears, nose and tongue, and the three ruupas of solidity, temperature and motion which can be experienced through the door of the bodysense. Thus, there are altogether twelve gross ruupas. As we have seen, the sense objects have been classified separately, they are not included in dhammaaramma.na.
There are sixteen kinds of subtle ruupa and these have been classified as the second class of dhammaaramma.na. They include, for example, nutritive essence (ojaa), bodily intimation, kaaya-vi~n~natti, the ruupa which is the physical condition for expression through the body, such as gestures or facial expression, and vocal intimation, vacii-vi~n~natti, the ruupa which is the physical condition for speech or other ways of vocal intimation.