Iâm afraid there is nothing simple about it. Attempts so far have failed to show that there is a consistent logic behind the usage of manas, citta, and vinnana in the suttas - sometimes they mean similar phenonema, sometimes different, whereas citta and vinnana seem closer to each other than manas.
I think there is a similar ambiguity in the usage of the English words/concepts mind and consciousness except that we have the advantage of modern philosophy, linguistics, etc to hone in on more defined usable meanings. With Pali we are dealing with a dead thought world.
But all Iâm doing is playing at apologetics by showing that there is leeway to chuck pretty much anything I want into the range of manayatana since dhamma is such a potentially broad category. In other words, it is perfectly conceivable that anything that can be experienced that does not partake of the first 5 sensory-fields would have been included under the sensory-field of the mind by the Buddha. It isnât necessarily the case that this is so but it might still be the case.
Besides, there is one sutta I can cite which suggests that if the discourses on the 6 sense spheres and those on the arupas are not coming from two different schools of thought or one muddled thinker then the arupas must fall under the domain of manayatana.
At Savatthi. âBhikkhus, I will teach you the all. Listen to thatâŠ.
âAnd what, bhikkhus, is the all? The eye and forms, the ear and sounds, the nose and odours, the tongue and tastes, the body and tactile objects, the mind and mental phenomena. This is called the all.
âIf anyone, bhikkhus, should speak thus: âHaving rejected this all, I shall make known another allââthat would be a mere empty boast on his part. If he were questioned he would not be able to reply and, further, he would meet with vexation. For what reason? Because, bhikkhus, that would not be within his domain.â - SN 35.23
Somaratne writes here (p.185) that manas and vinnana are being âperfumed by cittaâ - as maddeningly poetic this is where weâd hope for clarity Iâm afraid this really gets as concrete as the suttas are.
I tend to see the suttas as being at times pretty loosey-goosey with terminology. Presumably because that terminology was already being used in a rough, perhaps semi-nebulous, manner, or because the Buddha or the compilers didnât see any need to be too analytical or rigorous in defining their terms, or both.
I donât pretend to have a solution for that (because the suttas donât), but understanding ayatana as locus of experience we cannot assume either that ayatanas are like babushkas: an ayatana within an ayatana within an ayatana. Nowhere do the suttas say that the endless-space-ayatana is within manayatana. A more simple reading (to me at least) is that leaving the salayatana results in reaching the ÄkÄsÄnañcÄyatana.
Iâm not saying their is some babushka hierarchy of ayatanas going on, just that words can be used in different ways. If I said that a football field was in my field of vision that would make perfect sense but I wouldnât usually speak that way. Instead Iâd say I was at a football field and it would be implied that the football field was in my visual field, assuming the person I was talking to knew I wasnât blind. I can imagine that it is similarly implied that if someone says they had been dwelling in ÄkÄsÄnañcÄyatana that they were having a kind of purely mental experience, that they were in contact with some dhamma via manayatana.
And again Iâd refer to the sutta above to suggest that the simpler reading is to include ÄkÄsÄnañcÄyatana within manayatana unless we assume that the suttas on the arupas and those on the six sense spheres come from different authors or one muddle-minded author.