Those who have attained to the highest stage of rūpa-jhāna and see the disadvantages of rūpa-jhāna which is still dependent on materiality, might want to cultivate arūpa-jhāna or 'immaterial jhana'. There are four stages of arupa-jhana. The first stage of arūpa-jhāna is the 'Sphere of Boundless Space' (ākāsānañcāyatana). In order to attain this stage of arūpa-jhāna one has to attain first the highest stage of rūpa-jhāna in any one of the kasina meditations excepting the 'kasina of limited space' and achieve mastery in it. We read in the 'Visuddhimagga' (X, 6):
'When he has seen the danger in that [fine-material fourth jhana in this way
and has ended his attachment to it, he gives attention to the 'Base consisting
of Boundless Space' as peaceful. Then, when he has spread out the kasina to
the limit of the world-sphere, or as far as he likes, he removes the kasina
(materiality) by giving his attention to the space touched by it, (regarding
that) as 'space' or 'boundless space'.
As regards the 'Sphere of Boundless Space', the 'Visuddhimagga' (X, 6)
explains the 'removing' of the kasina:
'And when the kasina is being removed, it does not roll up or roll away. It is
simply that it is called 'removed' on account of his non-attention to it, his
attention being given to 'space, space'. This is conceptualized as the mere
space left by the removal of the kasina (materiality) ...'
In this way he can surmount the materiality of the kasina and attain the
first arūpa-jhāna, the Sphere of Boundless Space'. The second stage of arūpa-
jhāna is: the 'Sphere of Boundless Consciousness'
(viññānañcāyatana). The meditation subject of this stage of arūpa-jhāna is
the consciousness which is the first arūpa-jhāna. The person who wants to
attain this stage of arūpa-jhāna should first achieve 'mastery' in the 'Sphere of
Boundless Space'; he should see the disadvantages of this stage and end his
attachment to it. We read in the 'Visuddhimagga' (X, 25):
'...So having ended his attachment to that, he should give his attention to the
base consisting of boundless consciousness as peaceful, adverting again and
again as 'Consciousness, consciousness', to the consciousness that occurred
pervading that space (as its object)...'