"Monks, this recitation of more than 150 training rules comes every fortnight, in reference to which sons of good families desiring the goal train themselves. [1] There are these three trainings under which all that is gathered. Which three? The training in heightened virtue, the training in heightened mind, the training in heightened discernment. [2]
"There is the case where a monk is wholly accomplished in virtue, moderately accomplished in concentration, and moderately accomplished in discernment. With reference to the lesser and minor training rules, he falls into offenses and rehabilitates himself. Why is that? Because I have not declared that to be a disqualification in these circumstances. But as for the training rules that are basic to the holy life and proper to the holy life, he is one of permanent virtue, one of steadfast virtue. Having undertaken them, he trains in reference to the training rules.
"With the wasting away of [the first] three fetters, he is one who has seven more times at most. Having transmigrated and wandered on among devas and human beings, he will put an end to stress.
"[Or] he is one going from good family to good family [i.e., rebirth in the human realm or any of the deva realms]. Having transmigrated and wandered on among two or three good families, he will put an end to stress.
"[Or] he is one with one seed. Having arisen only once more in the human realm, he will put an end to stress.
"[Or], with the wasting away of [the first] three fetters, and with the attenuation of passion, aversion, & delusion, he is a once-returner who — on returning only once more to this world — will put an end to stress.
"There is the case where a monk is wholly accomplished in virtue, wholly accomplished in concentration, and moderately accomplished in discernment. With reference to the lesser and minor training rules, he falls into offenses and rehabilitates himself. Why is that? Because I have not declared that to be a disqualification in these circumstances. But as for the training rules that are basic to the holy life and proper to the holy life, he is one of permanent virtue, one of steadfast virtue. Having undertaken them, he trains in reference to the training rules.
"With the wasting away of the five lower fetters, he is one going upstream to the Peerless [the Akaniṭṭha heaven, the highest of the Pure Abodes.][3]
"[Or], with the wasting away of the five lower fetters, he is one unbound with fabrication [of exertion].
"[Or], with the wasting away of the five lower fetters, he is one unbound without fabrication [of exertion].
"[Or], with the wasting away of the five lower fetters, he is one unbound on arrival [in a Pure Abode]. [4]
"[Or], with the wasting away of the five lower fetters, he is one unbound in between.
"There is the case where a monk is wholly accomplished in virtue, wholly accomplished in concentration, wholly accomplished in discernment. With reference to the lesser and minor training rules, he falls into offenses and rehabilitates himself. Why is that? Because I have not declared that to be a disqualification in these circumstances. But as for the training rules that are basic to the holy life and proper to the holy life, he is one of permanent virtue, one of steadfast virtue. Having undertaken them, he trains in reference to the training rules. With the ending of effluents, he dwells in the effluent-free awareness-release and discernment-release, having directly known and realized them for himself right in the here-and-now.
"Those who are partially accomplished attain a part; those who are wholly accomplished, the whole. The training rules, I tell you, are not in vain."
The Commentary defines this category and the following one with this example: Suppose that a non-returner appears spontaneously in the Aviha (Not Falling Away) Pure Abode, where the lifespan is 1,000 eons. If he/she attains unbinding after the first 100 eons, he/she is classed as one unbound on arrival. If he/she attains unbinding anywhere from between the first day in that Pure Abode up through the first 400 eons, he/she is classed as one unbound in between. For a non-returner appearing spontaneously in any of the higher Pure Abodes, where the lifespans get progressively longer, the same proportions would hold.
This way of classifying these two categories, however, doesn't make much sense for two reasons. (a) The sutta lists the categories in ascending order, and there's little reason to class one who takes 400 eons to attain unbinding higher than one who takes only 100 eons to do so. (b) The second category actually includes the first, so there would seem to be little reason to distinguish them as two separate categories.
It would make better sense to define the categories this way: One who attains unbinding relatively soon after arriving in a Pure Abode is one unbound on arrival. One who attains unbinding after leaving the human realm but before reaching a Pure Abode would be one unbound in between.