arupa-raga: "desire for the formless", the seventh fetter.
Arupa means without form.
The arupa-khandhas are feeling, perception, sankharas (mental) and consciousness.
There are four arupa-jhanas. These are the four highest states of meditation in which there is no perception of or consciousness of form. Beings who succeed in achieving any of these find them more satisfactory than physical existence or existence in the heaven worlds of form. When they die, they generally arise in the plane of existence which corresponds to the particular jhana they have attained. Life on these planes is very long.
The Buddha's former teachers are still there. They arose there because they did not find anything higher. They thought this was the ultimate. But on these planes, too, you arise (get born) and, after a time, you fall away from them (die) and are born again somewhere else as the result of latent, unfulfilled karma.
More birth, more death. These are the characteristics of all planes of existence except Nibbana, which is the highest. Hence, although there is no suffering in these states or these worlds, the fact that they are impermanent makes them unsatisfactory and the desire for them constitutes a fetter.
Even for non-meditators, when one just sits and thinks, the actual process of thinking is formless, though what one thinks about may involve objects of sense and desire for them (kama-raga) or delight in forms perceived through the eye or ear (rupa-raga). However, certain types of thinking, where the mind is quite detached and without feelings either for or against the content of the thoughts, are arupa. Pure mathematics is arupa, for example when one is simply concerned with number and not relating it to actual objects (forms). That is, one is not thinking of five apples divided among three people, but simply 5 divided by 3.
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