From "The Four Right Exertions" in The Wings to Awakening, Thanissarohttp://www.accesstoinsight.org/lib/auth ... ml#part2-c
There are these four right exertions. Which four? There is the case where a monk generates desire, endeavors, arouses persistence, upholds & exerts his intent for the sake of the non-arising of evil, unskillful qualities that have not yet arisen... for the sake of the abandoning of evil, unskillful qualities that have arisen... for the sake of the arising of skillful qualities that have not yet arisen... (and) for the maintenance, non-confusion, increase, plenitude, development, & culmination of skillful qualities that have arisen. These are the four right exertions.
Just as the River Ganges flows to the east, slopes to the east, inclines to the east, in the same way when a monk develops & pursues the four right exertions, he flows to Unbinding, slopes to Unbinding, inclines to Unbinding.