| | howdy odl. i think the question is a bit strange, myself. at the second jhana vitaka / vikara (really efforting your attenion upon the object) drop away and leads to the ease that defines that jhana. one is still focused but the effort falls away or diminishes to the background. that is classice jhana description.
vipassana is parsing all of this stuff , seeking and differentiating the distinctions which come up. the one is a solidifying practice the other a dissembling process if you will.
to say that this is the "only common factor" is, i think innacurate. there are factors that are often not mentioned in the simplified descriptions of jhanas like "singleness of mind" which exist o up through the jhanas.
tom |