I’m not sure about the northern Agamas, but in the suttas and in Vedic literature we find:
Pāli
Rūpa
- form
- figure
- appearance
- principle of form
Sanskrit
रूप [ rūpa ]
- any outward appearance or phenomenon or colour
- form
- shape
- figure
- dreamy or phantom shapes
This comes from the thematic verb रूप् (rūp) which is in the 10th Gaṇa:
√ रूप् [ rūp ]
- to form
- figure
- represent
Sadly I cannot locate any Proto Indo European roots as of yet. Still, without this the meaning of rūpa here is quite clear. It is the “image” or “form” that occurs at contact. Based on this understanding rūpa-khandha would then not be the physical body, but the image of the body at contact. We do see this distinction between rūpa and the physical body in the suttas:
"'This body of mine is endowed with form, composed of the four primary elements, …
ayaṃ kho me kāyo rūpī cātumahābhūtiko …"
The body is one thing, rūpa is another. This would make little sense if rūpa was the physical body, or even if it meant “matter”. Regarding the 4 mahābhūta in the upaniṣadaḥ they started out as deities, thus being rather abstract:
सेयं देवतैक्षत हन्ताहमिमास्तिस्रो देवता अनेन जीवेनात्मनानुप्रविश्य नामरूपे व्याकरवाणीति ॥ ६.३.२ ॥
seyaṃ devataikṣata hantāhamimāstisro devatā anena jīvenātmanānupraviśya nāmarūpe vyākaravāṇīti || 6.3.2 ||
- That god [Existence] decided: ‘Entering into these three deities [fire, water, and earth], as the individual self, I shall manifest myself in many names and forms’.
Chāndogyopaniṣad
In the suttas they are no longer deities, but they are still abstract qualities. For example, examining the body in relation to the earth element means examining it in the sense of hardness or softness. This is the noticing of a phenomenal experience, rather than being a theory of matter. The Abhidhamma/Abhidharmas took a different view, which is in line with their more metaphysical and ontological nature.
Can we say the order of the six sense-organs (eye, ear, nose, tongue, body and mind) is arranged according to its involvement in perception of material forms from high to low?
I’m not sure about the order, but I’m sceptical of translating āyatana as “sense organ”:
Āyatana (आयतन)
- resting place
- support
- seat
- place
- home
- house
- abode
I won’t delve into the roots with this one. It is said then there are 6 Āyatana:
- Cakkhāyatanaṃ
- Sotāyatanaṃ
- Ghānāyatanaṃ
- Jivhāyatanaṃ
- Kāyāyatanaṃ
- Manāyatanaṃ
1. Cakkhu
According to Monier-Williams Sanskrit Dictionary (the dictionary I have been using throughout) we find:
Cakṣu (चक्षु)
- the eye
Yet, when we look at the Proto-Indo-European root we find:
√kʷeḱ
- To see
-To look
In the suttas we very often find the following:
“The arising and vanishing of the eye is evident,
Cakkhussa uppādopi vayopi paññāyati.” MN 148
Or
“Mendicant, if someone meditates observing rise and fall in the eye faculty, they grow disillusioned with the eye faculty.
“Cakkhundriye ce, bhikkhu, udayabbayānupassī viharanto cakkhundriye nibbindati … pe …" SN 35.154
Now, does it even make sense to say one dwells observing the “rise and fall” of the eye, be it eye or eye faculty? I would submit it does not. It does however make sense if we translate cakkhu in accordance with its Proto-Indo-European root of “kʷeḱ”, that is to say “vision”. For the physical “eye” the suttas use “akkhi” from the sanskrit “ákṣi”:
akṣi (अक्षि)
- the eye
- the number two
This is the same meaning we find in the PIE root:
√h₃ókʷs
- the eye
I would repeat the same arguments for the other sense bases (excluding the mind). The āyatana then are the abodes/domains where sensual beings like humans are found, between “vision & forms” etc since this is what we seek and grasp hold of (and when there is grasping, there is a being). I see this as being more in line with the Buddha’s overall epistemology and general outlook rather than “sense bases” and “eye and forms” which is, once again, more of an Abhidhamma perspective.