Ven. Bikkhu Bodhi:
From Venerable Bodhi
There definitely seem to be suggestions in the suttas that there is a temporal gap, an intermediate state, between lives, at least with respect to rebirth in the human realm and in the case of non-returners. I have a long note to the Connected Discourses of the Buddha (Samyutta Nikaya), chapter 46, which explores this question in regard to the fivefold distinction among non-returners. I will paste it in below.
The position that rebirth is instantaneous is strongly maintained by the Theravada commentaries, but other schools of Indian Buddhism based on the early collections (pre-Mahayana) supported an intermediate state. This became a ground of contention among the Buddhist schools, sometimes generating a lot of emotional friction, but the issue seems to be given very little importance in the early discourses. Nevertheless, there are passages that suggest (quite clearly, in my opinion) that there is an intermediate state. For example, the famous Metta Sutta speaks of extending loving-kindness to 'bhuutaa vaa sambhavesii vaa' -- "to beings who have come to be and those about to come to be" -- and the suttas on nutriment say that the four kinds of nutriment are "for the maintence of those that have come to be and to assist those about to come to be." Those beings that are sambhavesii, "about to come to be" (or "seeking existence") must be an allusion to those in the intermediate state seeking a new rebirth.
See too SN 44:9, in which Vacchagotta asks the Buddha: "When a being has laid down this body but has not yet been reborn in another body, what does Master Gotama declare to be its fuel on that occasion?" The Buddha does not reject V's question by asserting that such a situation is impossible. He says, rather, that in such a situation "I declare that it is fueled by craving.382 For on that occasion craving is its fuel."
Note 382 reads:
382. Tam aha˙ ta˚hÒp›d›na˙ vad›mi. The Buddha’s statement seems to imply that a temporal gap can intervene between the death moment and reconception. Since this contradicts Therav›da orthodoxy, Spk contends that at the death moment itself the being is said to be “not yet reborn” because the rebirth-consciousness has not yet arisen.
I have also found evidence for beings in this state from the reported rebirth memories of people who (without meditative experience) can recollect their previous life and death. Several cases I have read of this type report that the being, after passing away, spends some time moving about in a subtle body (identical in form with their previous body, hence with a sense of the same personal identity) until they find themselves drawn towards a particular couple, who then become their new parents. Some cases like this are included in Francis Story's book, Rebirth as Doctrine and Experience (published by the Buddhist Publcation Society, Kandy, Sri Lanka).
See too Peter Harvey's book, The Selfless Mind (Curzon) which I refer to in the note below.
65 This fivefold typology of nonreturners recurs at 48:15, 24, 66; 51:26; 54:5; and 55:25. Spk explains the antar›parinibb›yı (“attainer of Nibb›na in the interval”) as one reborn in the Pure Abodes who attains arahantship during the first half of the life span. This type is subdivided into three, depending on whether arahantship is reached: (i) on the very day of rebirth; (ii) after one or two hundred aeons have elapsed; or (iii) after four hundred aeons have elapsed. The upahaccaparinibb›yı (“attainer of Nibb›na upon landing”) is explained as one who attains arahantship after passing the first half of the life span. For Spk, the asaºkh›raparinibb›yı (“attainer without exertion”) and the sasaºkh›raparinibb›yı (“attainer with exertion”) then become two modes in which the first two types of nonreturners attain the goal. This explanation originates from Pp 16–17 (commented on at Pp-a 198–201). However, not only does this account of the first two types disregard the literal meaning of their names, but it also overrides the sequential and mutually exclusive nature of the five types as delineated elsewhere in the suttas (see below).
If we understand the term antar›parinibb›yı literally, as it seems we should, it then means one who attains Nibb›na in the interval between two lives, perhaps while existing in a subtle body in the intermediate state. The upahaccaparinibb›yı then becomes one who attains Nibb›na “upon landing” or “striking ground” in the new existence, i.e., almost immediately after taking rebirth. The next two terms designate two types who attain arahantship in the course of the next life, distinguished by the amount of effort they must make to win the goal. The last, the uddha˙sota akani˛˛hag›mı, is one who takes rebirth in successive Pure Abodes, completes the full life span in each, and finally attains arahantship in the Akani˛˛ha realm, the highest Pure Abode.
This interpretation, adopted by several non-Therav›da schools of early Buddhism, seems to be confirmed by the Purisagati Sutta (AN IV 70–74), in which the simile of the flaming chip suggests that the seven types (including the three kinds of antar›parinibb›yı) are mutually exclusive and have been graded according to the sharpness of their faculties. Additional support comes from AN II 134,25–29, which explains the antar›parinibb›yı as one who has abandoned the fetter of rebirth (upapattisa˙yojana) without yet having abandoned the fetter of existence (bhavasa˙yojana). Though the Therav›din proponents argue against this interpretation of antar›parinibb›yı (e.g., at Kv 366), the evidence from the suttas leans strongly in its favour. For a detailed discussion, see Harvey, The Selfless Mind, pp. 98–108.
AN II 155–56 draws an alternative distinction between the sasaºkh›raparinibb›yı and the asaºkh›raparinibb›yı: the former reaches arahantship through meditation on the “austere” meditation subjects such as the foulness of the body, the perception of the repulsiveness of food, discontent with the whole world, the perception of impermanence in all formations, and mindfulness of death; the latter, through the four jh›nas.