It is not uncommon for people to walk through glass windows and doors. Yet it would not be a problem for someone with some paint to have drawn pictures on that glass – and it might have saved some hospital trips. I realize they probably didn’t have glass back in Buddhas time but it is a reason why using invisible these days might not make the meaning completely clear (so to speak).
MN 21 presents four similes – each with a similar format – basically someone is trying to carry out a task which by its nature is impossible. There is a kind of foolishness with respect to each one – they are just trying to do something that can’t work:
- the image of someone furiously digging so as to remove all the earth of the earth
- the image of someone – paints in hand – trying to paint pictures in empty space
- the image of someone – with a bundle of burning grass – trying to boil all the water in the Ganges
- the image of someone trying to make a soft supple bag crackle and rattle
To try to paint pictures in empty space seems foolish – you are standing there waving your paint brush around and it isn’t doing anything - there is no way to get something to stick – to make an impression.
In contemporary usage we wouldn’t normally say that empty space is invisible even though it is. If I ask you to pay attention to the ghost in front of you then you might say “I can’t see it” (it’s invisible) but if I ask you to pay attention to the empty space in front of you, you probably won’t say “I can’t see it”. You can attend to that space – it is defined by it’s emptiness.
There is another sutta (AN 3.130) that deals with a very similar theme. And here there is the sense of inscriptions on different surfaces – progressively less permanent: stone, soil, and water. It describes three types of individuals in the world while MN 21 presents an ideal to strive for: no imprint at all.
In DN 11, saying something like “Where consciousness is invisible, boundless, all-luminous ” sounds strange in that one would not normally say something is invisible and then go on to describe it. So ‘without surface’ seems reasonable to me though I get the sense more of non-reactive, un-impressionable, non-supportive, untouchable, unimpactable.
The phrase in my view is pointing to the imperturbability of the Arahant as well as the spacious and luminous quality of consciousness that I see mentioned by some of our contemporary Arahants. For example:
“Consciousness arises in the mind, purely and simply without producing suffering. …All sense media and the sense contact that they condition are just naturally occurring phenomena that exist according to their own intrinsic characteristics. They have no negative effect whatsoever on the citta that has successfully completed its task”
“This subtle awareness manifests as a radiance that extends forth in all directions around us”
– Ajahn Maha Boowa
“Knowing is the normality of mind that’s empty, bright, pure, that has stopped fabricating, stopped searching, stopped all mental motions — having nothing, not attached to anything at all.”
“All that remains is pure, clean, bright — great emptiness, enormously empty” - Ajahn Dune Atulo