Full understanding as investigation (tírana parinna) is panna that
thoroughly investigates nama and rupa, without preference for any particular
nama or rupa, without selection of them. Panna realises the characteristics of
realities as they appear through all six doors and thus it can see them as only
dhammas. When panna clearly realises that all nama and rupa are equal, in
this respect that they are only dhammas, it becomes more accomplished.
Thus it can realise the fourth stage of insight, knowledge of the arising and
falling away of nama and rupa. Full understanding of investigation begins
at this stage.