To put it in a monk’s words:
In sammā·saṅkappa, we find abyāpāda·saṅkappa and avihiṃsā·saṅkappa (besides nekkhamma·saṅkappa). I still can’t see why is there a need to include avihiṃsā·saṅkappa. Shouldn’t abyāpāda·saṅkappa cover it?
I have been wondering the same thing for a while, and judging by the number of hits on the corresponding thread at DhammaWheel, so do quite some people.
The answer appeared to me while staying in a monastery where when it rains there are lots of snails crossing the paths, and if we are not careful enough, we easily crush them unintentionally. Then it stroke me that harming others does not necessarily happens intentionally.
Then the difference between avihiṃsā·saṅkappa and abyāpāda·saṅkappa could just be intention: there is harming others intentionally (with byāpāda) and unintentionally (without byāpāda, therefore not covered by abyāpāda).
One example could be that of Jain ascetics sweeping their path wherever they go to make sure they are not going to step on any insect. There would have been no ill will against the insect, just harming out of carelessness, so they felt compelled to do this. Another example is when a monk gathers wood for the fire to wash/dye robes: he might put it in a place where ants or insects won’t settle inside, in order to prevent them from being harmed. The harm would have also taken place without ill-will, just out of expediency, as it seems to be allowed by the Vinaya, according to Thanissaro Bhikkhu.
Then abyāpāda·saṅkappa would be the aspiration of non ill will or benevolence, and avihiṃsā·saṅkappa would be the aspiration not to harm others, even unintentionally, which expresses itself by making choices to that end, like organizing oneself to inflict minimum harm on animals, (for lay people) becoming vegetarian or not buying from industries that resort to exploitation of poor people etc.
If I am not mistaken, the Visuddhimagga relates abyāpāda·saṅkappa (aspiration of non ill will) to mettā·ceto·vimutti (liberation of the mind through good will) and avihiṃsā·saṅkappa (aspiration of not harming) to karuṇā·ceto·vimutti (liberation of the mind through compassion), which does make some sense. Those are defined as follows:
SN 42.8
« That disciple of the noble ones — thus devoid of covetousness, devoid of ill will, unbewildered, alert, mindful — keeps pervading the first direction with an awareness imbued with good will, likewise the second, likewise the third, likewise the fourth. Thus above, below, & all around, everywhere, in its entirety, he keeps pervading the all-encompassing cosmos with an awareness imbued with good will — abundant, expansive, immeasurable, without hostility, without ill will. Just as a strong conch-trumpet blower can notify the four directions without any difficulty, in the same way, when the awareness-release through good will is thus developed, thus pursued, any deed done to a limited extent no longer remains there, no longer stays there. »« That disciple of the noble ones — thus devoid of covetousness, devoid of ill will, unbewildered, alert, mindful — keeps pervading the first direction with an awareness imbued with compassion, likewise the second, likewise the third, likewise the fourth. Thus above, below, & all around, everywhere, in its entirety, he keeps pervading the all-encompassing cosmos with an awareness imbued with compassion — abundant, expansive, immeasurable, without hostility, without ill will. Just as a strong conch-trumpet blower can notify the four directions without any difficulty, in the same way, when the awareness-release through compassion is thus developed, thus pursued, any deed done to a limited extent no longer remains there, no longer stays there. »