The eye cannot see itself; to do this a mirror is needed, but what it sees is not itself, only its reflection. Vijnana may devise some means to recognize itself, but the recognition turns out to be conceptual, as something postulated.
Prajna, however, is the eye that can turn itself within and see itself, because it is the law of identity itself. It is due to Prajna that subject and object become identifiable, and this is done without mediation of any kind.
Vijnana always needs mediation as it moves on from one concept to another---this is in the very nature of Vijnana. But Prajna, being the law of identity itself, demands no transferring from subject to object.
--- D. T. Suzuki