For this has been said:
...So in many hundred suttas there is only mentality-materiality which is illustrated, not a being, not a person. Therefore, just as when the component parts (of a chariot) such as axles, wheels, frame, poles... are arranged in a certain way, there comes to be the mere conventional term ‘chariot’, yet in the ultimate sense, when each part is examined, there is no chariot ... so too, when there are the five khandhas of clinging there comes to be the mere conventional term ‘a being’, ‘a person’, yet in the ultimate sense, when each component is examined, there is no being as a basis for the assumption ‘I am’ or ‘I’; in the ultimate sense there is only mentality-materiality. The vision of one who sees in this way is called correct vision.
Furthermore, nāma has no efficient power, it cannot occur by its own efficient power ...It does not eat, it does not drink, it does not speak, it does not adopt postures. And rūpa is without efficient power; it cannot occur by its own efficient power. For it has no desire to eat, it has no desire to drink, it has no desire to speak, it has no desire to adopt postures. But it is when supported by rūpa that nāma occurs; and it is when supported by nāma that rūpa occurs. When nāma has the desire to eat, the desire to drink, the desire to speak, the desire to adopt a posture, it is rūpa that eats, drinks, speaks and adopts a posture...
...Its function is to make a sign as a condition for perceiving again that “this is the same”, as carpenters, etc., do in the case of timber...
“A hard thing there is, O King, which the Blessed One has done.” “And what is that?” “The fixing of all those mental conditions which depend on one organ of sense, telling us that such is contact, such is feeling, such is saññā (perception), such is volition and such is citta.” “Give me an illustration.” “Suppose, O King, a man were to wade down into the sea, and taking some water in the palm of his hand, were to taste it with his tongue. Would he distinguish whether it were water from the Ganges, or from the Jamunā, or from the Aciravatī, or from the Sarabhū, or from the Mahī?” “Impossible, Sir.” “More difficult than that, great King, is it to have distinguished between the mental conditions which follow on the exercise of any one of the organs of sense!”