I agree, that in conventional conversation internal and external is applicable:
Kaccāna, this world mostly relies on the dual notions of existence and non-existence. 2.2But when you truly see the origin of the world with right understanding, you won’t have the notion of non-existence regarding the world. 2.3And when you truly see the cessation of the world with right understanding, you won’t have the notion of existence regarding the world. Kaccayanagotta sutta
In terms of insight such clear demarcations are disturbed when causally arisen experiences make up the world.
I’m a bit of a science nerd also, so I like that general scheme too. Matter (and its phases), energy and space-time cover most things in physics, and I suppose energy and matter are inter-convertible also. We can lump energy and things like light under the fire element. Even space kind of fits under the air element category (even though that occasionally gets separate billing as an element in its own right in places, as your link points out).
I also like an Analayo’s approach (mentioned earlier also) where things like bone/teeth/nails are firmly in the earth category, blood/bodily fluids are in water, breathing etc. is in air and bodily temperature is in fire. You can also apply this to what’s coming into the body (what sustains the body): air, beverages, solid food, things to regulate heat/cold (clothes, shelter etc.), and even what comes out of the body (I won’t go into that )!
Thanks everyone, it’s been a useful discussion and I’m planning to do a session on the elements with my local group.
I think I’m right in saying that we don’t experience the four great elements of form directly, rather we experience sense-objects which are derived from them, ie sights, sounds, tactile sensations, odours and flavours.
I think the closest one can get to the four elements is tactile sensation via the skin, eg wind = a cool, light varying pressure on the skin.
I would say form needs to be consisted of elements according SN12.2. Remember that there is also formless realm that doesn’t need form. Concious can still function without needing form as long as feelings, perceptions, and volition formations are still there.
“And what are name and form? Feeling, perception, intention, contact, and attention. This is called name. The four primary elements, and form derived from the four primary elements. This is called form. Such is name and such is form. These are called name and form.“ SN 12.2