A + B → C, where A stands for a physical sense base such as the eye, B stands for a physical sense object such as a tree, and C stands for consciousness of the object.
People eel wriggle infinitely on this issue to ostensibly make Theravada idealist or phenomenalist. However one cannot do so with a very simple expression like this.
Obviously, and undeniably, saying A and B depend on C for their existence, or are purely imaginary and thus composed of or created by C is ridiculous. C does not exist unless A and B are added together.
It would be like saying a man born and raised from a mother and father exists before the parents do. Nonsense.
There are many linguistic games to be played about consciousness and reality. None of them apply to the simple expression A + B → C.
And this expression is conclusively how consciousness works in the Buddha’s own words:
Bhikkhus, consciousness comes to be in dependence on a dyad. And how, bhikkhus, does consciousness come to be in dependence on a dyad? In dependence on the eye and rupa there arises eye-consciousness.
-SN 35.93
The eye (A) + rupa (B) → consciousness (C).
There is simply no way around this to make the dhamma into idealism. Physical external reality necessarily precedes consciousness. You cannot have eye consciousness before or without the physical eye and external rupa.
A given instance of perceptual consciousness is said to arise only in dependence upon two conditions: the sense organ and its corresponding object-field. This implies that perceptual consciousness arises only in conjunction with an appropriate and existent object; perceptual consciousness of a nonexistent object or without an object is, therefore, impossible.
-Disputed Dharmas
Early Buddhist Theories on Existence
Collett Cox
p 136-137
Another ostensible way to get around this is to say that the Buddha taught, as the Mahayana do, that eye consciousness, rupa, and the eye arise in dependence on each other. That rupa and the eye never arise without dependence on consciousness.
First, the sutta quoted does not allow for that. It explicitly and clearly says consciousness depends on the eye and rupa making contact. It does not say they all arise simultaneously and depend on each other.
Second, in another sutta the Buddha explicitly clarifies that external rupa and the eye exist independently of consciousness.
If, friends, internally the eye is intact but no external rupa come into its range, and there is no corresponding conscious engagement, then there is no manifestation of the corresponding section of consciousness. If internally the eye is intact and external rupa come into its range, but there is no corresponding conscious engagement, then there is no manifestation of the corresponding section of consciousness."
-MN 28
A and B exist even when C does not arise. Thus, idealism and phenomenalism are incoherent interpretations of the dhamma. There is no such thing as either because rupa exists independent of consciousness. In idealism rupa is consciousness, and in phenomenalism rupa is merely sense data and perception that has no existence independently. Hence, when rupa precedes consciousness and perception both positions are impossible.
Lastly, the Buddha also made it abundantly clear that the very idea that external reality depends on consciousness is absurd. Including even distant visible objects like stars. It all exists even for a blind man who has no consciousness of it. The implication is that to say otherwise is silly.
Student, suppose there were a man born blind who could not see dark and light forms, who could not see blue, yellow, red, or carmine forms, who could not see what was even and uneven, who could not see the stars or the sun and moon. He might say thus: ‘There are no dark and light forms, and no one who sees dark and light forms; there are no blue, yellow, red, or carmine forms, and no one who sees blue, yellow, red, or carmine forms; there is nothing even and uneven, and no one who sees anything even and uneven; there are no stars and no sun and moon, and no one who sees stars and the sun and moon. I do not know these, I do not see these, therefore these do not exist.’ Speaking thus, student, would he be speaking rightly?”
“No, Master Gotama. There are dark and light forms, and those who see dark and light forms…there are the stars and the sun and moon, and those who see the stars and the sun and moon. Saying, ‘I do not know these, I do not see these, therefore these do not exist,’ he would not be speaking rightly.”
“So too, student, the brahmin Pokkharasāti is blind and visionless.
-MN 99
From here the eel wriggling invariably slides into flowery, poetic, or vague sutta quotes that can be ostensibly interpreted to support idealism. However, the matter is conclusively decided by these very clear, technical suttas that do not rely on poetic interpretation or vagueries .
And, of course, the Abhidhamma, Visuddhimagga, and commentary tradition agrees.
All form is that which is…
void of idea,
neither feeling, nor perception, nor synthesis,
disconnected with thought,”
“form exists which is not due to karma having been wrought”-Dhammasangani 2.2.3
They are states (dhamma) owing to bearing (dháraóa) their own characteristics
and owing to their so bearing (dháraóa) for the length of the moment appropriate
to them.39
39. This alludes to the length of duration of a moment of matter’s existence, which is
described as seventeen times as long as that of consciousness (see Vibh-a 25f.).
-Visuddhimagga XI.104
It is the dhammas alone that possess ultimate reality: determinate existence “from their own side” (sarupato) independent of the minds conceptual processing of the data.
-Bhikkhu Bodhi, A Comprehensive Manual of Abhidhamma