The third stage of arūpa-jhāna is the 'Sphere of Nothingness' (ākāsānañcāyatana). We read in the 'Visuddhimagga' (X, 32) that the person who wants to attain this stage should give his attention to the present non-existence of the past consciousness which pervaded the 'boundless space' and which was the object of the second stage of arūpa- jhāna, the 'Sphere of Boundless Consciousness'. We read (X, 33):
'Without giving further attention to that consciousness, he should (now)
advert again and again in this way 'There is not, there is not', or 'Void, void',
or 'Secluded, secluded', and give his attention to it, review it, and strike at it
with thought and applied thought'.
Further on (X, 35) we read:
'...he dwells seeing only its non-existence, in other words its departedness
when this consciousness has arisen in absorption'.
The fourth arūpa-jhāna is the 'Sphere of Neither Perception Nor Non-
Perception' (neva-saññā-nāsaññāyatana). The object of this jhāna is the third
stage of arūpa-jhāna. We read in the 'Visuddhimagga' (X, 49):
'The word meaning here is this: that jhāna with its associated states neither
has perception nor has no perception because of the absence of gross
perception and presence of subtle perception, thus it is 'neither perception
nor non-perception' (neva-saññā-nāsaññam)'.
Further on (X, 50) we read:
'...Or alternatively: the perception here is neither perception, since it is
incapable of performing the decisive function of perception, nor yet non-
perception, since it is present in a subtle state as a residual formation,
thus it is 'neither-perception-nor-non-perception'...
It is also explained that the feeling arising with this jhāna-citta is 'neither-
feeling-nor-non-feeling' (since it is present in a subtle state as a residual
formation); the same applies to consciousness, contact (phassa) and the
other cetasikas arising with the jhānacitta.